Meaning: Waves are disturbances that transfer energy through space, in this case, referring to light waves.

Wrong options:

• sight: The word 'sight' refers to the ability to see, which does not fit as it does not describe a form of motion.
• fall: 'Fall' is a verb that does not relate to the subject of light and does not fit grammatically in this context.
• needs: 'Needs' is a noun that refers to requirements or necessities, which does not fit as it does not describe a form of motion.
• arrested: 'Arrested' is a past participle that describes an action taken on something, which does not fit as a subject here.
• shades: 'Shades' refers to variations of color or darkness, which does not relate to the concept of light as a form of motion.
• motion: 'Motion' is a noun that describes movement but does not fit as it is not a plural subject in this context.
• depend: 'Depend' is a verb that indicates reliance, which does not fit as it does not describe a form of motion.

Correct answer: arrested

Explanation: The word 'arrested' is a past participle that describes the action of stopping or capturing the waves of light. It fits grammatically as it describes what happens to the waves in relation to the pigment-cells of the retina.

Meaning: Arrested means to stop or capture something, in this case, the light waves being stopped by the pigment-cells.

Wrong options:

• sight: 'Sight' is a noun that refers to the ability to see, which does not fit as it does not describe an action taken on the waves.
• fall: 'Fall' is a verb that does not relate to the action of stopping light waves and does not fit grammatically in this context.
• needs: 'Needs' is a noun that refers to requirements, which does not fit as it does not describe an action taken on the waves.
• waves: 'Waves' is a noun that refers to the subject of the sentence, which does not fit as it does not describe an action.
• shades: 'Shades' refers to variations of color or darkness, which does not relate to the action of stopping light waves.
• motion: 'Motion' is a noun that describes movement but does not fit as it does not describe an action taken on the waves.
• depend: 'Depend' is a verb that indicates reliance, which does not fit as it does not describe an action taken on the waves.

Correct answer: motion

Explanation: The term 'motion' refers to the state of being in movement, which is the result of the transmutation of light waves. It fits grammatically as a noun that completes the idea of what form the waves are converted into.

Meaning: Motion refers to the act or process of moving or being moved.

Wrong options:

• sight: 'Sight' refers to the ability to see, which does not fit as it does not describe a form of movement resulting from light.
• fall: 'Fall' is a verb that does not relate to the concept of movement and does not fit grammatically in this context.
• needs: 'Needs' is a noun that refers to requirements, which does not fit as it does not describe a form of movement.
• arrested: 'Arrested' is a past participle that describes an action, which does not fit as it does not describe a form of movement.
• shades: 'Shades' refers to variations of color or darkness, which does not relate to the concept of movement resulting from light.
• waves: 'Waves' is a noun that refers to the subject of the sentence, which does not fit as it does not describe the result of the conversion.
• depend: 'Depend' is a verb that indicates reliance, which does not fit as it does not describe a form of movement.

Correct answer: needs

Explanation: The word 'needs' refers to the requirements or necessities that creatures have for survival. It fits grammatically as a plural noun that serves as the object of the sentence, aligning with the context of discussing what is required by creatures.

Meaning: Needs refer to the essential requirements or necessities for survival.

Wrong options:

• sight: 'Sight' refers to the ability to see, which does not fit as it does not describe a requirement or necessity.
• fall: 'Fall' is a verb that does not relate to the concept of requirements and does not fit grammatically in this context.
• arrested: 'Arrested' is a past participle that describes an action, which does not fit as it does not describe a requirement.
• waves: 'Waves' is a noun that refers to the subject of the sentence, which does not fit as it does not describe a necessity.
• shades: 'Shades' refers to variations of color or darkness, which does not relate to the concept of requirements.
• motion: 'Motion' is a noun that describes movement but does not fit as it does not describe a necessity.
• depend: 'Depend' is a verb that indicates reliance, which does not fit as it does not describe a requirement.

Correct answer: fall

Explanation: The word 'fall' is a verb that indicates the action of not occurring or not happening. It fits grammatically as it describes the relationship between existence and vision in the context of the sentence.

Meaning: Fall means to not occur or to not happen, in this case, referring to the absence of vision in certain creatures.

Wrong options:

• sight: 'Sight' refers to the ability to see, which does not fit as it does not describe an action related to vision.
• needs: 'Needs' is a noun that refers to requirements, which does not fit as it does not describe an action related to vision.
• arrested: 'Arrested' is a past participle that describes an action, which does not fit as it does not describe an action related to vision.
• waves: 'Waves' is a noun that refers to the subject of the sentence, which does not fit as it does not describe an action related to vision.
• shades: 'Shades' refers to variations of color or darkness, which does not relate to the action of not occurring in relation to vision.
• motion: 'Motion' is a noun that describes movement but does not fit as it does not describe an action related to vision.
• depend: 'Depend' is a verb that indicates reliance, which does not fit as it does not describe an action related to vision.