黎明前开孔
参考答案：
每天早上3点钟左右，未成熟的上、中部叶就会出现气孔显著开张现象，称为黎明前开孔。
(2013·湖南，34)—I don't understand why you didn't go to the lecture yesterday afternoon.
—I'm so sorry.But I________my homework.
A．had done
B．was doing
C．would do
D．am doing
试述光合磷酸的机理。
