自发性气胸最常见的症状是（）
A.胸痛
B.呼吸困难
C.咳嗽
D.咳痰
E.休克
参考答案：A
（10分）如图所示电路中,电源的电动势E=10V,内电阻r =1Ω，已知R1 =3Ω,R2 =6Ω,
C = 30μF,试求:
⑴闭合开关S,待稳定后通过R1的电流.
⑵将开关S断开,这以后流过R1的电量.
We____ Chinese. So you and I have black eyes and black hair. [ ]
A. all are
B. are all
C. are both
D. both are
