____Our dance club wants a dancer. If you are interested in dancing, you can join our club.

____We need five students to help repair bikes for students in our school.

____Our college radio station needs four reporters. If you have experience in it, you can join us.

____Our school soccer team wants two coaches. If you want to get the job, please call 88556677.

____Our city library needs a librarian. We want a woman.

A. Celina started to learn to dance when she was five years old. She dances well. She wants to join a dance club.

B. Sam was a soccer player one year ago. He wants to work as a soccer coach.

C. Jerry is interested in reporting and he has much experience. He was a news reporter when he was in high school.

D. Ken is good at writing. He has published two books. He wants to be a famous writer.

E. Victory can repair bikes. He learned to mend bikes from his father. He wants to help the students repair their broken bikes.

F. Jenny is 35 years old. She is a quiet woman and she used to work for a school library.

如图所示，正方形线圈abcd谢绕对称轴OO′在匀强磁场中匀速转动，转速为 $\frac{50}{\pi }r/s$ ，已知ab=ad=20cm，匝数N=100，磁感应强度B=1T，图示位置线圈平面与磁感线平行．闭合回路中线圈的电阻r=4Ω，外电阻R=12Ω．求：

硝酸铵受热或高温条件下易分解，其反应化学方程式为：2NH₄NO₃=2N₂↑+O₂↑+4X，则X的化学式为（　　）