换流站无功功率控制措施有()。
A.投切换流站装设的无功补偿设备
B.直流功率调制
C.换流变分接头调整
D.换流器触发角的快速相位控制
参考答案:A, C, D
—Your classroom is really bright and clean.
—It _____ after school every day. [ ]
A. is cleaned
B. cleaned
C. was cleaned
造成第二、三跖骨颈疲劳骨折的原因多是()。
A.直接暴力
B.间接暴力
C.肌肉过度强烈收缩
D.持续劳损
E.骨质疏松