下列有关人体性别决定的叙述,正确的是( )
A:生男生女的机会不相等
B:卵细胞中性染色体组成为XY
C:体细胞中不含性染色体
D:生男生女是由男性决定的
每逢暴雨,贵州山区容易引发的地质灾害是( )
Last week he borrowed a book from the library. Today he has to return it to the library.