"error CS1501: No overload for method `Add' takes `2' arguments"

I have been trying to build the following Text Adventure and have reached an error that I cannot figure out how to resolve. The error is as follows : 'Assets/My_Scripts/MH_Script.cs(19,23): error CS1501: No overload for method Add' takes 2' arguments'

and here is MH_ScriptManager:

Can somebody please explain to me what I am doing wrong, and how I can go about resolving this error in the future. I have only been coding for a month, it's fun but very meticulous.