Many people agree that   knowledge of English is a must in   international trade today.

A．a；／

B．the；an

C．the；the

D．／；the

下列属于非离子型表面活性剂的是

A．胆酸钠

B．吐温80

C．十二烷基硫酸钠

D．油酸三乙醇胺

E．卵磷酯