变压器绝缘自投入运行后，在允许条件下运行，其寿命可达（）年。
A.25～30
B.20～25
C.15～20
D.10～15
参考答案：B
Which of the following statements about unemployment is least accurate（）
A. Frictional unemployment is unemployment due to changes in the economy that prevent qualified workers from being immediately matched with existing job openings.
B. The economy is said to be operating at full employment only if there is no cyclical or frictional unemployment in the economy.
C. The economy is said to be operating at full employment when cyclical unemployment is zero.
各级瓜叶菊种子含水量不高于（）。
A、7%
B、9%
C、10%
D、11%
