题目内容

矩阵式变频电路输出电压可利用单相输入、三相输入相电压、三相输入线电压构造

A. 对
B. 错

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矩阵式变频电路优点

A. 输出电压可控制为正弦波，频率不受电网频率的限制。
B. 输入电流也可控制为正弦波且和电压同相，功率因数为1，也可控制为需要的功率因数。
C. 能量可双向流动，适用于交流电动机的四象限运行。
D. 不通过中间直流环节而直接实现变频，效率较高。

短文填空，然后从各个小题所给的A、B、C、D四个选项中选出最佳选项。(每道小题2分)I1every student will feel nervous before they take the exam, since exam is very important for students. And the teachers will assess the students based on it, so all the students want to perform well in the 2. Anxiety makes students find it hard to fall asleep well, as they are afraid of 3it. Also,it makes the students feel worry and lower their energy. Experts suggest that sharing can be a way to 4 such problems. Exercise more will help you relax and manage emotions . Eating lots of fruit and vegetables helps improve one’s physical condition.In conclusion，It is better to find the proper ways to calm feeling of anxiety before 5for exams.

（）是在线路中断时跨越障碍的主要承载结构

A. 支座系统
B. 桥跨结构
C. 墩台基础
D. 桥墩

（）是支承桥跨结构并将恒载和车辆等活载传至地基的构筑物，也叫下部结构并且设置在桥两端。

A. 支座系统
B. 墩台基础
C. 桥台
D. 桥墩