The correct answer is Option B.
We are to use the correct form of the verb DO in the given sentence.
IS is the form of the verb BE.
HAS is used in the meaning of possession (not intended in the given sentence).
Hence Option C and D are ruled out as the correct answers.
Option A - DOESN'T is the form of the verb DO but it is used with a noun in the singular, TROUSERS is in the plural. Hence it is incorrect.
Thus, Option B- DON'T is the grammatically correct answer that completes the sentence as 'DON'T' is a plural verb.