Using a class in another script

Script A:

Class testingClass

Dim a

End Class

 

Script B:

‘USEUNIT Script A

Dim instance

Set instance = New testingClass   ‘Here I got the error: the variable testingClass is undefined

 

My purpose is to create a Script which could store all classes, so they could be used in other scripts.

Could anyone give me some clue? Thanks in advanced.