fso在asp中怎么判断一个txt是空的？？

whichfile=server.mappath("read.txt")
Set fso = CreateObject("Scripting.FileSystemObject")
Set txt = fso.OpenTextFile(whichfile,1)
While Not txt.AtEndOfStream
rline =txt.ReadLine'读取一行
if left(rline,1)='A' then
b=split(rline," ",-1,1)'用空格截取序号
aa=b(1)
bb=b(3)
cc=b(5)
dd=b(7)
else
changdu=len(rline)'判断一行的长度
a=split(rline," ",-1,1)'用空格截取序号
id=trim(a(0))'用空格截取序号
changdu2=len(id)'序号长度
question=mid(rline,changdu2,changdu-changdu1-1)'截取题目
answer=right(rline,1)

end if

sql="insert into "&表&"("id,question,answer,a,b,c,d) values('"&id&"','"&question&"','"&answer&"'&"','"&a&"','"&"','"&aa&"','"&"','"&bb&"','"&"'