His grandparents used to a walk after dinner but now they are used to a walk after brea

问题补充：

His grandparents used to a walk after dinner, but now they are used to a walk after breakfast.

A. take, take

B. taking, taking

C. taking, take

D. take, taking

答案：

A. take, take

B. taking, taking

C. taking, take

(答案→)D. take, taking

解析：考察固定搭配，used to do sth 过去常常做某事 be used to doing sth习惯于做某事，句意：他的祖父母过去常常晚饭后去散步，但是现在他们习惯早饭后散步。故选D