手工加热弯管的操作顺序是（）。
A、划线—灌沙—弯曲
B、灌沙—划线—弯曲
C、划线—灌沙—加热—弯曲
D、灌沙—划线—加热—弯曲
参考答案：C
关于萃取剂，下列说法正确的是（）。
A、对与溶液中被萃取的溶质有显著的溶解能力，对稀释剂必须不溶
B、挥发度越大越好
C、界面张力越大越好
D、粘度大对萃取有利
The achievements of the greatest minds in science could never have been reached if it had not been for the patient and accurate work of hundreds of other people.
A．has it not been
B．if it had been
C．if hasn't been
D．had it not been
