The correct answer is A. don’t.
College students don’t usually wear a uniform. This is because college students are adults and are free to choose their own clothes. There are some colleges that have a dress code, but this is usually not a uniform.
Option B, didn’t, is incorrect because it is in the past tense. The question is about what college students usually do, not what they did in the past.
Option C, aren’t, is incorrect because it is in the present tense. The question is about what college students usually do, not what they are.
Option D, haven’t, is incorrect because it is in the present perfect tense. The question is about what college students usually do, not what they have done.