题目

16.It is no doubt that once ____ this city, you’ll find that there is so much surprise waiting for you to discover. visit        B. visiting      C. visited    D. to visit 答案：B 解析: 本句话为省略，once后省略了you are，所以选择visiting。如图5－8所示，在河岸上用细绳拉船，为了使船匀速靠岸，拉绳的速度应是怎样的？