Two questions and no trickery:

>! Ask the 1st guard "Does your door lead to certain death?"
>! <br />
>! Ask the 2nd guard "Does the 1st guard's door lead to certain death?"

Take these actions depending on their answers:

>! 1. Yes and yes, they are both telling the truth, use a different door.
>! <br />
>! 2. Yes and no, one of them is telling the truth, use a different door.
>! <br />
>! 3. No and yes, one of them is telling the truth, use a different door.
>! <br />
>! 4. No and no, both are telling the truth, use that door.