电压有（）之分。
A.正电压
B.大电压
C.负电压
D.小电压
参考答案：A, C
用所给词的适当形式填空。
1. I have a pair of _______ (sock).
2. Henry_______ (have)a School Day this year.
3. These are my_______ (photo).
4. September is the _______ (nine) month of the year.
5. There_______ (be)a baseball and some books on the desk.
首选的检查为
A．静脉胆道造影B．BUSC．CTD．PTCE．核素扫描
