I think she is ______ at dancing than singing. [ ]
A. better
B. good
C. well
D. best
答案:A
从平面a外一点P引与a相交的直线,使得P点与交点的距离等于1,则满足条件的直线条数一定不可能是( )。
A.0条
B.1条
C.2条
D.无数条
常减压装置常用的阀门有(例五种)(),(),(),(),()。