vbs读取TXT每一行并赋值到变量a

vbs代码:

Dim fso,f,a
Set fso = CreateObject("Scripting.FileSystemObject")
Set f=fso.OpenTextFile("D:\test.txt",1)
DO While f.AtEndOfStream <> True
 a=f.ReadLine 

 msgbox a
loop

test.txt内容

10899
10900
20000
20001
20002
20003