Meaning: 'Operated' means to control or manage the functioning of something, in this case, the elevators or hoists.

Wrong options:

• completed: 'Completed' implies finishing something, which does not fit the context of how elevators were used.
• provided: 'Provided' suggests supplying something, which does not accurately describe the action of using power to run the elevators.
• supported: 'Supported' indicates assistance or backing, which does not convey the active role of controlling the elevators.

Correct answer: developed

Explanation: The word 'developed' is the correct choice as it indicates the process of creating or improving something over time, fitting the context of how elevators evolved in the 1800s. It is also in the past tense, matching the narrative of the sentence.

Meaning: 'Developed' means to bring something into a more advanced or effective state, referring to the evolution of the elevator design.

Wrong options:

• established: 'Established' suggests setting something up, which does not capture the ongoing process of improvement implied here.
• constructed: 'Constructed' refers specifically to building something, which does not encompass the broader concept of evolution and improvement.
• created: 'Created' implies bringing something into existence, but does not convey the idea of gradual advancement as effectively as 'developed'.

Correct answer: gravity

Explanation: The term 'gravity' is the correct answer as it refers to the natural force that pulls objects downward, fitting perfectly in the context of how the cab lowers when water is removed. It is a noun that aligns with the mechanics described in the sentence.

Meaning: 'Gravity' is the force that attracts a body toward the center of the earth, explaining how the cab descends.

Wrong options:

• power: 'Power' is a general term that does not specifically describe the natural force acting on the cab in this context.
• magnitude: 'Magnitude' refers to size or extent, which does not relate to the action of lowering the cab.

Correct answer: system

Explanation: The word 'system' is appropriate as it refers to a set of connected things or parts working together, which aligns with the description of how the valves and ropes functioned in the elevator context. It fits grammatically and contextually as a noun.

Meaning: 'System' means a group of related parts that work together, in this case, the mechanism used to control the elevator.

Wrong options:

• order: 'Order' implies a sequence or arrangement, which does not accurately describe the mechanical setup of the elevator.
• apparatus: 'Apparatus' refers to a complex structure or equipment, but does not convey the organized functionality implied by 'system.'
• approach: 'Approach' suggests a method or way of doing something, which does not fit the context of describing the mechanical setup.

Correct answer: appeared

Explanation: The word 'appeared' is the correct choice as it indicates the emergence of something in the past, fitting the historical context of the sentence. It is in the past tense, aligning with the narrative about the development of elevators.

Meaning: 'Appeared' means to come into view or become visible, referring to the introduction of the traction elevators.

Wrong options:

• secured: 'Secured' implies making something safe or fixed, which does not fit the context of the introduction of a new type of elevator.
• emerged: 'Emerged' suggests coming out or becoming known, but does not convey the same sense of visibility as 'appeared.'
• acquired: 'Acquired' means to gain possession of something, which does not accurately describe the introduction of a new technology.