问题
One of the most important things ineducation is to let students ____ positive emotions and experience in theprocess of their learning
A:stepped a tall man in his thirties
B:a tall man in his thirties stepped
C:did a tall man in his thirties step
D:did a tall man step in his thirties
B:a tall man in his thirties stepped
C:did a tall man in his thirties step
D:did a tall man step in his thirties
正确答案是：
