基尔霍夫第一定律可以表述为：流过任意一个节点电流的（）为零。
A、之和
B、之差
C、代数和
D、数值
参考答案：C
—Tomorrow is my birthday. Would you like to come to dinner, Vince?
—_________. I have to look after my grandpa, he is ill in hospital. [ ]
A. No, I wouldn't.
B. Sure, I would love to.
C. I'm sorry, but I can't.
D. Oh, happy birthday to you.
（）
A.1
B.2
C.3
D.4
（）