下列命题中，属于定义的是[ ]
A.两点确定一条直线
B.同角或等角的余角相等
C.两直线平行，内错角相等
D.点到直线的距离是该点到这条直线的垂线
答案：D
—How old is the bridge over there?
—Oh, very old. It _____ about three hundred years ago. [ ]
A. is built
B. was built
C. is building
D. has built
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