richachampion wrote:Without adequate amounts of sleep, people's newly acquired skills and also new factual information may not get properly encoded into their memory circuits.

(A) Without adequate amounts of sleep, people's newly acquired skills and also
(B) Without the adequate amount of sleep they need, people's newly acquired skills and even
(C) If they do not have adequate amounts of sleep, people's newly acquired skills and even
(D) If people do not get adequate amounts of sleep, newly acquired skills and even
(E) If people do not get the adequate amount of sleep they need, newly acquired skills and also

A and B: Without sleep, people's skills and information may not get encoded
These options convey that people's SKILLS AND INFORMATION require sleep to get encoded.
This meaning is nonsensical.
Eliminate A and B.

If an introductory pronoun lacks an antecedent, the referent for the pronoun must be the SUBJECT of the following clause.
C: If they do not have sleep, people's skills and information may not get encoded
Here, they (an introductory pronoun without an antecedent) seems to refer to skills and information (the subject of the following clause), conveying that SKILLS AND INFORMATION do not have sleep.
This meaning is nonsensical.
Eliminate C.

E: the adequate amount of sleep they need
Here, the portions in red are redundant:
an ADEQUATE amount of sleep = the NEEDED amount of sleep.
Eliminate E.

The correct answer is D.