They are looking forward to Beijing.A. visitB. visitedC. visitsD. visiting

问题补充：

They are looking forward to Beijing.

A. visit

B. visited

C. visits

D. visiting

答案：

A. visit

B. visited

C. visits

(答案→)D. visiting

解析：考查非谓语动词.句意:他们正盼望着参观北京.短语look forward to doing sth盼望做某事,to是介词,后面接名词或者动名词作宾语 ，故选D