—Simon, I wonder _______.

—Last Saturday.

A．when the foreign visitors arrived

B．when did the foreign visitors arrive

C．when the foreign visitors will arrive

D．when will the foreign visitors arrive

⁶⁰钴治疗机定时器误差不大于（）

A.1%

B.2%

C.3%

D.2.5%

E.1.5%