光周期现象是指植物生长发育对（）的反应。
A.昼夜长短不同
B.昼夜长短相同
C.昼长夜长
D.昼短夜短
参考答案：A
化简：2(a+1) －a= ▲ .
___ _ make progress, she has been studying hard.
A．So as to
B．In order to
C．So that
D．In order that
