How can I use string replacement to replace multiple, variable strings? I am currently doing it this way: 

```
 > $a = "a"
 > $b = "b"
 > $c = "c"
 > $d = "d"
 > $e = "e"
 > $f = "f"
 > $g = "g" 
 > "abcdefg" -replace $a -replace $b -replace $c -replace $d -replace $e -replace $f -replace $g 

```

How can we do this with only one `-replace` statement?