小勇利用如图所示的实验装置“探究导体在磁场中运动时产生感应电流的条件”，他将实验中观察到的现象记录在如表中．

    This is a map of our school. There are1 buildings in our school: a library, an office building, a class building, a dinging hall and a sports hall. The library is2the left of the class building. There3many books in the library. We study in the class building, and after class, we often read books in the4. Our teachers work in the5 . This is a building6 twelve offices. Four teachers are in one office. Our school is old,7we have a big sports hall. We8 in it. What's your favourite9? Let's play it in the sports hall. I 10 my school very much. It's very good.

牛的体细胞有30对染色体，那么牛的精子、卵细胞和受精卵中分别含染色体数是（　　）