Meaning: 'Develop' means to grow or progress in a certain way, indicating that babies change their crying habits as they mature.

Wrong options:

• envolve: 'Envolve' is not a standard English word and does not fit grammatically or contextually in this sentence.
• change: While 'change' is a valid verb, it does not convey the gradual process of growth as effectively as 'develop' does in this context.
• alter: 'Alter' implies a modification but lacks the connotation of growth or progression that 'develop' provides.

Correct answer: having

Explanation: The word 'having' is the correct gerund form that fits grammatically and contextually, indicating the state of experiencing a good cry. It aligns with the structure of the sentence, which discusses the benefits of crying.

Meaning: 'Having' refers to the experience or possession of something, in this case, the experience of a good cry.

Wrong options:

• doing: 'Doing' suggests an action but does not fit the context of experiencing a state or condition as effectively as 'having'.
• making: 'Making' implies creation or causation, which does not align with the context of experiencing a good cry.
• getting: 'Getting' suggests obtaining something, which does not accurately convey the experience of crying.

Correct answer: contain

Explanation: The word 'contain' is grammatically correct and contextually appropriate, indicating that tears hold or include a natural painkiller. It fits well within the scientific context of the sentence.

Meaning: 'Contain' means to hold or have something within, indicating that tears include the substance enkaphalin.

Wrong options:

• retain: 'Retain' implies keeping something already possessed, which does not fit the context of tears including a substance.
• hold: While 'hold' could work, it is less precise than 'contain' in this context, which specifically refers to the inclusion of a substance.
• keep: 'Keep' suggests possession over time, which does not accurately describe the relationship between tears and the substance they include.

Correct answer: fighting

Explanation: The word 'fighting' fits grammatically and contextually, indicating an active struggle against sorrow and pain. It aligns with the idea of combating negative emotions, making it the most suitable choice.

Meaning: 'Fighting' means to struggle against something, in this case, sorrow and pain, suggesting an active effort to overcome these feelings.

Wrong options:

• struggling: 'Struggling' is similar but does not convey the same active connotation as 'fighting', which implies a more vigorous effort.
• opposing: 'Opposing' suggests resistance but lacks the emotional connotation of actively dealing with sorrow and pain as 'fighting' does.
• striking: 'Striking' does not fit contextually as it implies hitting or making an impression, which is unrelated to the emotional context of the sentence.

Correct answer: produce

Explanation: The word 'produce' is grammatically correct and contextually appropriate, indicating the act of generating or creating enkaphalin. It fits well within the scientific context of the sentence regarding the body's response to weeping.

Meaning: 'Produce' means to create or generate something, in this case, the natural painkiller enkaphalin as a result of weeping.

Wrong options:

• construct: 'Construct' implies building or forming something, which does not fit the context of generating a chemical in the body.
• achieve: 'Achieve' suggests reaching a goal, which does not accurately describe the process of generating a substance like enkaphalin.
• provide: 'Provide' implies supplying something to someone else, which does not fit the context of the body generating its own painkiller.