He was thinking about the problem when a
问题:
He was thinking about the problem when an apple fell off the tree, _____ him right on the head.[ ]
A. hit
B. having hit
C. hitting
D. and hitting
He was thinking about the problem when an apple fell off the tree, _____ him right on the head.[ ]
A. hit
B. having hit
C. hitting
D. and hitting