问题补充：
—How does Jack usually go to school?
--Hea bike, but now hethere to keep healthy.
A. used to riding, is used to walk
B. was used to riding, is used to walking
C. used to ride, is used to walking
D. used to ride, is used to walk
答案：
A. used to riding, is used to walk
B. was used to riding, is used to walking
(答案→)C. used to ride, is used to walking
D. used to ride, is used to walk
解析：used to do sth,过去常常做某事，be used to doing sth,习惯于做……，结合句意：—杰克通常怎样去上学？- 他过去常常骑自行车去，但是为了健康他习惯于步行去。故选C。
