如图为某小型水电站的电能输送示意图，发电机通过升压变压器T1和降压变压器T2向用户供电，已知输电线的总电阻R=10Ω，降压变压器T1的原、副线圈匝数之比为4：1，副线圈与用电器R0组成闭合电路．若r真、r真均为理想变压器，T2的副线圈两端电压u=220 sin 100πt（V），当用电器电阻R0=11Ω时（ ）A．通过用电器凡的电流有效值为20 A B．升压变压器的输入功率为4650 W C．发电机中的电流变化频率为100 Hz D．当用电器的电阻R0减小时，发电机的输出功率减小  |
答案：B
| 阅读理解。读一读，选择正确答案。 |
| L: Hi, Steven! How are you? S: I'm fine. Thanks. And you? L: I'm fine, too. Today is my birthday. Please come to my birthday party tonight. S: Happy birthday to you, Li Ming! What's the date today? L: Today is August twelfth. S: How old are you? L: I'm eleven years old. S: What is your address? L: My address is 268 Ninth Avenue. S: Look! This is for you. L: Birthday present! A black and white football! I like it very much. Thank you. |
| 1. When is Li Ming's birthday? |
[ ] |
| A. On August ninth. B. On August twelfth. |
| 2. How old is Li Ming? |
[ ] |
| A. Nine years old. B. Eleven years old. |
| 3. What is Li Ming's address? |
[ ] |
| A. 268 Ninth Avenue. B. 286 Ninth Avenue |
| 4. What is Li Ming's birthday present? |
[ ] |
| A. Football. B. Basketball. |
| 5. What colour is the football? |
[ ] |
| A. Black. B. Black and white. |