Professor Smith，along with his assistants，on the project day and night to meet the deadline
A.work　　　　　　B.workingC.is workingD.are working在线课程C
该句主语是Professor Smith，故谓语动词用单数。当together with，as well as，no less than，rather than，but，except，along with，like，besides，as much as，more than...连接两个主语时，谓语动词要与前面的主语保持一致。