A:6
B:3
C:−3
D:−6
牵牛花清晨开放,这种现象说明生物具有的特征是( )
a3•a4•a+(a2)4+(﹣2a4)2.
Chinese is ___ a useful language _____ more and more foreigners want to learn it.
如图,在地面上的点A处测得树顶B的仰角α=75°,若AC=6米,则树高BC为( )