为保证冷却效果，管状结构变压器冷却器每年应进行（）次冲洗，并宜安排在（）来临前进行。
参考答案：1～2；大负荷
单句改错
1. To my delighted, I passed the examination.
2. Hearing the news, he feels very delighting.
3. It is delight for me to help those poor children.
4. They were delighted at that the conference had been called off.
管道线路、人（手）孔井维护规范中，对管道管孔维护要求是（）。
A.无损坏
B.无阻塞
C.无淤泥
D.无杂物
