He’ll accept the job _______the salary is very low. After all he needs money.

A．unless

B．if not

C．though

D．so long as

图为电工常用的克丝钳，它的设计和使用应用了很多物理知识。其中钳把包了一层胶皮是为了__________，钳把做的比钳口长是为了____________________。