牙 * * 形成（）
A.牙釉质
B.牙本质和牙髓
C.牙本质
D.牙骨质
E.牙槽骨
参考答案：B
如图所示电路，已知电源电压为6V，R1的阻值为2Ω，R2的阻值为3Ω，R3的阻值为6Ω．求：
（1）S1、S2都闭合时电流表的示数；
（2）S1、S2都断开时电路的总功率．
________ good time we had at the party last night!
Yes. It was ________ exciting party that I would never forget it.
A．What, so
B．How, such
C．What a, such an
D．How a, so an
