题干
-- Are they about to have dinner?
-- Yes, it ______ in the dining room
A：is being served
B：is severed
C：is serving
D：serves
答案(点此获取答案解析）
A
-- Are they about to have dinner?
-- Yes, it ______ in the dining room
A：is being served
B：is severed
C：is serving
D：serves
C上的函数满足
，则
=