原式=x2-y2xy•xx+y
=(x+y)(x-y)xy•xx+y
=x-yy．
It was ________ he came back from Africa that year ________ he met the girl he would like to marry.[ ]
A. when; then
B. not; until
C. not until; that
D. only; when
车床能完成哪些工作？
