Umma, accompanied by her brother, . . . . . . . . at the party. A. is B. are C. was D. were

The correct answer is: C. was

The sentence is in the past tense, because it is talking about an event that happened in the past. The subject of the sentence is “Umma”, which is singular, so the verb must also be singular. The only singular option is “was”, so that is the correct answer.

The other options are incorrect because they are not in the past tense. Option A, “is”, is in the present tense. Option B, “are”, is also in the present tense. Option D, “were”, is in the past tense, but it is plural, which does not agree with the singular subject “Umma”.