单选题 The professor, together with several students, ______ working in the laboratory this time last week.
【正确答案】 C
【答案解析】[考点] 时态的用法及主谓一致
[解析] this time last week说明了此题的时态是过去进行时，A together with B结构做主语时，谓语动词的单复数与A保持一致。