A:①②
B:②③
C:①③
D:②④
亚洲分布最广的气候类型是____ 。
I have done everything possible to prevent him from running the risk but ______.
设P是双曲线x2a2-y2b2=1(a>0 ,b>0)上的点,F1、F2是焦点,双曲线的离心 率是54,且∠F1PF2=90°,△F1PF2面积是9,则a + b=( )