列写节点方程时，图示部分电路中B点的自导为：().
A．7S
B．-14S
C．5S
D．4S
参考答案：C
解析：
选电流源4A串联的2S不能算入。
根据句意及首字母或汉语提示完成单词。
1. Mary has no m____ to buy the book.
2. Mr. Brown works in a h____. He is a doctor.
3. Jim is too y____．He can't go to school.
4. Our teachers work ____(努力地), and we all like them.
5. Don't play in the street. It's ____ (危险的)．
“城市群”的出现是（）的特征。
A.古代城市
B.封建城市
C.近代城市
D.现代城市
