To prepare for the Olympic Games in summer London its largest ever exercise to test the

问题补充：

To prepare for the Olympic Games in summer, London its largest ever exercise to test the response of emergency services.

A. planned

B. is planning

C. had planned

D. plans

答案：

A. planned

(答案→)B. is planning

C. had planned

D. plans

解析：考查时态。根据句意：为了准备今年夏天的奥运会，伦敦正在计划一个有史以来最大的锻炼来检查对紧急服务的回应。