—Have you seen Dr. Adams recently?

—No. He __________ Hong Kong for an international meeting. He’ll come back tomorrow.[ ]

A. has gone in          

B. has been in          

C. has gone to        

D. has been to

精度要求较高或地面不够平坦时，应利用（）测放已知直线的垂线。

A.经纬仪

B.直角三角形法

C.水准仪

D.等腰三角形法