题目

30. _____in a science competition, the three students were awarded scholarships totaling $ 21, 000. A. To be judged the best         B. Judged the best   C. Having judged the best       D. Judging the best 答案：B2．小阳设计了一个天然气泄漏检测电路，如图甲所示，R为气敏电阻，其阻值随天然气浓度变化曲线如图乙所示，R0为定值电阻，电源电压恒定不变．则下列说法正确的是（　　）A．天然气浓度减小，电压表示数变小B．天然气浓度增大，电流表示数变小C．天然气浓度减小，电路消耗的总功率变大D．天然气浓度增大，电压表与电流表示数的比值变小