小麦倒伏以后会造成减产．施用下列哪种肥料对预防小麦倒伏有一定作用（ ）
A．氮
B．磷
C．钾
D．锌
答案：C
Can you believe his reason for being absent from the class _____ he had to look after his sick mother at home?
A．while B．that C when D．as
存款人开立单位银行结算账户，自正式开立之日起（ ）个工作日后，方可使用该账户办理付款业务。
A．2
B．3
C．5
D．7
