A:R1≤R2
B:R1≤
C:R1≥R2
D:R1≥
—_________ weather it is! We can't go boating on the Xuanwu Lake.
—Don't worry. Let's go to the Science Museum instead.
炎热的夏季中午,由于气孔关闭,光合作用反而下降。主要原因是( )