人体内含有性染色体的细胞是（ ）
A．体细胞
B．生殖细胞
C．受精卵
D．所有有细胞核的细胞
答案：D
若m2-n2=6，且m-n=3，则m+n=______．
— You look pale. What are you afraid of?
— ______. [ ]
A．To pass the dog
B．The dog standing there
C．Pass the dog
D．The dog is standing there
