用下列所给词的适当形式填空，每个字仅用一次。

Dear Sally,

Thanks for your photo. It is a nice one. Here 小题1:   a photo of my   小题2:. You   小题3: see four people in the photo.   小题4:  are my parents, my sister and I. My father is   小题5:      English teacher. My mother works in a   小题6: , too, but she isn’t a teacher. The girl beside me is my sister.   小题7:  name is Alice. We are students. Alice is in Class One and I’m in Class   小题8: . We  have a pet dog. Coco is the   小题9:  of our dog.   小题10:  is it? It is in front of my mother.

Yours 

Jenny

近交系动物繁殖的基本原则是保持近交系动物的（）。

A.生物学特性

B.生物多样性

C.基因纯合性

D.基因杂合性