计算z的值，当x大于等于y时，z=x；否则z=y。下列语句错误的是( )

A．If x＞=y Then z=x:z=y

B．If x＞=y Then z=x Else z=y

C．z=y:If x＞=y Then z=x

D．If x＜y Then z=y Else z=x