以下结算方式，进口商承担风险最高的是（）
A.预付货款
B.货到付款
C.信用证
D.托收
参考答案：A
下列各组混合气体中，比乙烯含碳量高的是（ ）
A．甲烷和丙烯
B．乙烷和丁烯
C．环丙烷与丙烯
D．丙烯与丙炔
--- Can I have a talk with you at about 5 this afternoon, Mr．Smith?
--- All right, I ______ to my office from a conference then．I will be waiting for you there．
A．have come back
B．will come back
C．will have come back
D．will be coming back
