（23）下列程序执行后，变量x的值为 。 Dim a,b,c,d As Single Dim x As Single a=10 b=30 c=400 I

（23）下列程序执行后，变量x的值为 。 Dim a,b,c,d As Single Dim x As Single a=10 b=30 c=400 If b>a Then d=a:a=b:b=d End If If b>c Then x=b Elself a>c Then x=c Else x=c End IfA.10 B.30 C.400 D.430