We should make a careful study of his.A. useful teaching experiencesB. useful teaching exp

问题补充：

We should make a careful study of his.

A. useful teaching experiences

B. useful teaching experience

C. usefully teaching experiences

D. usefully teaching experience

答案：

A. useful teaching experiences

(答案→)B. useful teaching experience

C. usefully teaching experiences

D. usefully teaching experience

解析：experience作“经验”解时，为不可数名词；用作可数名词时，意为“经历”。