A:Seeing; frightened
B:Seeing; frightening
C:Seen; frighte
D:To see; frightening
地球上最大的生态系统是( )
下列是计算氢氧化钙Ca(OH)2相对分子质量的式子,其中正确的是( )
Excuse me, sir. I bought the shoes yesterday, but they are in different sizes. One is size 37, _____is size 38.
已知OA→=(2,2),OB→=(4,1),OP→=(x,0),则当AP→·BP→最小时x的值是( )