下面程序是计算1+2+3+……+n值，此程序处划线处应填：Dim sum as long,I as integ……

下面程序是计算1+2+3+……+n值，此程序处划线处应填： Dim sum as long,I as integer,n as integer Sum=0 n=val(inputbox(“输入n的值”)) For i=1 to n ______ Next Iprint sum

A．sum=sum+i
B．n=n+i
C．sum=sum+1
D．n=n+1