Please answer its important to me

[helios]

Excellent!

[m4ster r0shi]

???

[Rabtherab]

You guys make me crack up.

[AngelHoof]

So.. Wait, Is it B or C?! or D?!

I thought it was C, but that's because I'm a psychic, and as such; mentally retarded.

[chrisname]

B is true, which means it must be behind D.

[m4ster r0shi]

Door A: It’s behind B or C
Door B: It’s behind A or D
Door C: It’s in here
Door D: It’s not in here

You know that only one of the inscriptions is true.

Suppose the spirit is behind door A. Then...

inscription A is false
inscription B is true
inscription C is false
inscription D is true

We have two true inscriptions, so it can't be A.

If you check B and C in the same way, you'll see that you can reject them too. Only D can be the right answer.

EDIT: As jmc noticed in his first reply.