Can anyone help explain to me why the answer to the following question is what it is.
The Navajo language is complex, with a structure and sound that makes it unintelligible to anyone without extensive exposure to it.
On the answer key, it states that answer is “make” and not “makes”. Can anyone explain why?
Although both singular make and plural makes could work, the simplest approach is to look at the two reasons that make the language hard to follow. Two reasons make it unintelligible.
The object pronoun ‘it’ (and its faraway subject antecedent ‘language’) does not come into play for the verb make, only its own subject (structure & sound) or subjects (structure and sound).
Structure and sound form two subjects. You could push it and say the structure and sound together form a barrier (a singular subject) to parsing Navajo, but since you say the answer key wants make, we can justify that answer.