松树体细胞的染色体数为24条，则它的性细胞的染色体数为（）。

A.48条

B.36条

C.24条

D.12条

Speaker A: Thank you for everything you've done for me during my stay here. Speaker B:______

A．Oh, this is what I should do.

B．You are welcome.

C．Don't say that. Actually I have done little for you.

D．I'm sorry for not having looked after you well.