_____the scientists have done lots of research on Mars, there is still much waiting to be discovered.
A:If
B:Since
C:Unless
D:Though
如图,BD,CE分别是△ABC的高,且BE=CD,求证:Rt△BEC≌Rt△CDB.
(1)计算:2cos60°-2×12-1+-3+2-10;
(2)解方程:1x-2=1-x2-x-3.
以下培养目标柏拉图最有可能赞许的是( )