The chairman of the department, together with some other teachers, ______a conference for the purpose of laying down certain regulations.
【正确答案】 A
【答案解析】解析：本题考查主谓一致和句子时态。句子的主语是the chairman，together with some other teachers是句中的插入语，不是主语，所以谓语动词用单数，选择A。