吃玉米棒子和葵花籽时,常发现玉米果穗再现“秃顶”、葵花籽出现空瘪现象.其主要原因都是( )
A:传粉不足
B:光照不足
C:开得花较少
D:肥料不足
计算:
Mr. Smith didn't go to the movie. He went swimming, ________.