MGMAT SC 4th Edition SC Question

[bkadia]

Can anyone please explain parallelism type/reason in solution to question 7 in problem set, chapter 4.

Question: We were dismayed to learn that our neighbors were untidy, disagreeable, and they were uninterested to make new friends.

Answer: We were dismayed to learn that our neighbors were untidy, disagreeable, and they were uninterested in making new friends.

[RonPurewal]

the difference between "uninterested to make" (incorrect) and "uninterested in making" (correct) is 100% pure idiom.
no logical rule at all here: the first is just unidiomatic (= incorrect by arbitrary convention), and the second is idiomatic (= correct by arbitrary convention).

the parallelism problem, however, lies in the presence of "they were". those words should NOT be there. (are they in the answer key? really? if so, then we've got a big big problem; please let us know, thanks)
reason:
"untidy" and "disagreeable" are adjectives.
the only way to complete the sentence with proper parallelism is to conclude the list with another adjective.

the correct form should thus be
We were dismayed to learn that our neighbors were untidy, disagreeable, and uninterested in making new friends.