Tom is on a visit _____ America.[ ]
A. to
B. at
C. in
D. on
答案：A
My sister met him at the Grand Theatre yesterday afternoon, so he ________ your lecture. [ ]
A. couldn’t have attended
B. needn’t have attended
C. mustn’t have attended
D. shouldn’t have attended
智能作业模式下飞行器飞至下一关键点指示灯（）。
A.紫灯5闪
B.蓝灯5闪
C.紫灯双闪
D.蓝灯双闪
