Question

The client's hospital stay was prolonged, _____ a super infection.
A. due to
B. because
C. instead of
D. do to

Answer 1

Due to means caused by which is used to modify the noun. We can use due to in a sentence if the sentence is correct when we replace due to with caused by. Here, super infection can be considered as a noun and due to can be used here as the meaning of the sentence will be correct if we replace with caused by.

Because is a subordinating conjunction, used in sentences to introduce a word for an explanation or reason which is followed by a subject or a verb. because of is a proposition which is followed by a noun or verb + ing form. Super infection can not be considered as a subject or verb.It can be considered as a noun. but the option has not given as because of. Thus option B can not be used in this sentence

Instead of means somethig replaced or in place of something. which can not be used here as the sentence want to say the reason of prolonged stay is superinfection.

do to is a phrasal verb. it canot be used as it is in a sentence.

Thus the answer is A. due to, The client's hospital stay was prolonged, due to a super infection.