. The purpose of the research had a more important meaning for them than ____.

A．ours

B．those of ours

C．it had for ours

D．it did for us

有性生殖的过程：当花粉落在雌蕊的______，在柱头分泌黏液的刺激下，花粉开始萌发，长出______，花粉管穿过雌蕊的______、______、到达子房的______，花粉管里的精子释放出来分别与______、______相融合，完成绿色开花植物的．双受精作用．