A:(1,10)
B:(5,6)
C:(20,24)
D:(10,12)
读岩石圈物质循环示意图,图中数码表示变质作用的是( )
下列应用及相应原理(用化学方程式表示)都正确的是( )
As teenagers,it is not until we are able to face difficulties bravely________we are mature enough.
若a→=1,b→=2,c→=a→+b→,且c→⊥a→,则a→与b→的夹角为 ( )
A. Today is Sunday.
B. He flies a kite.
C. The girl plays with her teddy bear.
D. We read books.
E. They play catch with a ball.