Hi @JayDee8732, thanks for your post. This is a Strengthen with Necessary Premise question.
The stimulus includes an argument:
P: Infants lack the motor ability required to voluntarily produce particular sounds.
P: Most children are several years old before they can voluntarily produce most of the vowel and consonant sounds of their language.
C: Speech acquisition is *entirely* a motor control process rather than a process that is abstract or mental.
This conclusion does not follow logically from the given premises.
Answer choice (A) identifies the necessary (and missing) premise: speech acquisition is a function *only* of one's ability to produce the sounds of spoken language.
If that is true, then, when added to the two premises supplied in the stimulus, you end up with a logically sound argument and a valid conclusion.
By contrast, if you were to negate answer choice (A), the argument in the stimulus falls apart. If speech acquisition is *not* only a function of one's ability to produce the sounds of spoken language, then it might involve abstract or mental processes, not just motor control processes.
Hope this helps! Please let us know if you have any additional questions.
