问题
选择题
—Your tea, please.
—There must be ________ in the tea. I like this kind of tea with sugar.[ ]
A. nothing sweet
B. something sweet
C. sweet something
D. sweet nothing
答案
答案：B
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—Your tea, please.
—There must be ________ in the tea. I like this kind of tea with sugar.[ ]
A. nothing sweet
B. something sweet
C. sweet something
D. sweet nothing
答案：B
目前，许多城市的十字路口都安装了太阳能红绿灯．白天太阳能电池板给红绿灯供电，同时多余的电能又给蓄电池充电．在阴雨天和晚上蓄电池又给红绿灯供电，使红绿灯能连续工作．其主要参数见下表
| 光电转换效率η | 有效受光面积S | 灯泡额定电压U |
| 40% | 0.5m2 | 24V |
（2）若太阳能红绿灯由红、黄、绿三灯组成．每天获得的电能，可使它连续正常工作40h，求：太阳能红绿灯正常工作时的功率和电阻．