化肥淡季商业储备贷款可以采用的用信方式是（）。
A.信用
B.保证担保
C.抵押
D.质押
参考答案：A, B, C, D
More than a dozen students in that school _______ abroad to study medicine last year.
A．sent
B．were sent
C．had sent
D．had been sent
只读字段声明为（）关键字。
