从所给的四个选项中,选择最合适的一个填入问号处,使之呈现一定的规律性。()
A.A
B.B
C.C
D.D
参考答案:C
He spoke proudly of his part in the game, without mentioning ________ his teammates had done.
A.what
B.which
C.why
D.while
牵引有效建立的条件?