how to write all values in text file . please look this issu

hi i am writing these text using windows service in vb.net.

It works fine when i write text like i am storing value for a="aaa" and writing in System.IO.File.WriteAllText("C:\test1.txt",a) . now if you open the test1.txt file you can see aaa.

but i need to write these 5 value in test1.txt.

a="abc"
b="bbb"
c="ccc"
d="ddd"
e="eee"

System.IO.File.WriteAllText("C:\test1.txt", a)
System.IO.File.WriteAllText("C:\test1.txt", b)
System.IO.File.WriteAllText("C:\test1.txt", c)
System.IO.File.WriteAllText("C:\test1.txt", d)
System.IO.File.WriteAllText("C:\test1.txt", e)

if i give like above, it ovewrites the all value . so, finally the nodepad(test1.txt) has e value only (ie, eee). so, how to write all these 5 value in test1.txt.

i mean if we open test1.txt file, it shoud have: aaa
bbb
ccc
ddd
eee

Please help.