Button Sequence Game

[captainghost]

Ive made a game where I want the user to push 4 buttons in a correct sequence in order to move on...Ive made everything so far except I dont know how to code it so the buttons will work like this...

I have 4 buttons...

btnA

btnB

btnC

btnD

What code would I use so the user has to press btnB, btnC, btnD, and btnA in the that order to move on?

Thanks in advance