The correct option is
B Have
In order to fill in the blank with the most appropriate verb, we must understand the 'subject and verb agreement'. A subject is a person, thing, or a concept, in a sentence. A sentence always describes a person, thing or a concept and that is called 'subject' of the sentence. The rest of the sentence is a complement (which has the object in it). A subject and a verb should always agree in a sentence. If the subject is singular (example: Raj), the verb will also be singular (does). If the subject is plural (We), the verb will also be plural (do).NOTE: In order to choose the best verb, let's find the subject first. The question mainly asks about the pants' state. Hence, 'blue pants' is the subject. As the subject is plural, the verb should be plural too.
Option A - Though 'has' is used as a 'be' verb to explain the state of being, it can't be used here as it is a singular verb. Hence, option A is incorrect.
Option C - 'Do' is a plural verb, but it is used to explain the act of 'doing' and not state of being. Hence, option C is incorrect.
Option D - 'Did' is a verb in past tense. As the verb in the question is in participle form, we can't use the helping verb in the 'simple past tense' form. Hence, option D is incorrect.
Option B - 'Have' is a plural verb and can be used with the plural subject. Also, it matches the tense of the sentence 'present perfect tense'. Hence, option B is the correct answer.
'Have you seen my blue pants?'