往井底安全阀（SSSV）加规定的油压，若不开应采取哪种措施好：（）
A、试加更高的油压
B、往油管正挤加压
C、往套管反挤加压
参考答案：B
下列实验基本操作中，正确的是
A．倾倒液体
B．过滤
C．加热液体
D．点燃酒精灯
After visiting China, most of the foreign friends said they would never forget the time _____ they had spent
in China.[ ]
A. what
B. that
C. when
D. at which
