I think you must be mistaken about seeing him at the theatre; I’m sure he ______ abroad all week.

A．is

B．was

C．has been

D．had been

请根据所学的力学知识将图中的现象分成两类，并写明分类的理由．一类为______（选填写字母），理由为力能改变物体的运动状态．另一类为______（选填写字母），理由为力能使物体产生形变．