A:受精卵和卵细胞
B:体细胞和精子
C:受精卵和体细胞
D:体细胞和卵细胞
物质发生物理变化的本质特征是( )
下列腺体中,属于内分泌腺的一组是( )
-- It's difficult for the village children to cross the river for school.
-- I think a bridge ________ over the river.