A:when; had come
B:that; have come
C:when; came
D:that; had come
植物进行有性生殖时,精子和卵细胞分别在( )里.
如果中央广播电台向外发射500kHz的电磁波,若距该台6000km处有一台收音机,求:
读数和写数都从____位起。
地理兴趣小组对某小流域进行水土流失的调查。在调查之前,该组同学需要优先收集调查区的地形图和( )