A good example would be as follows: My grandfather didn't attend last Christmas for he was dead.

When you describe a state, you can use 'be dead'.

Thanks Tracy! I thought about this question that if someone asked about my grandfather, I would say "he passed away/died at the age of 43" or simply "he is dead." I have no choice but to use present tense because it has become a fact. (In other words, if someone is dead, he is dead. Past tense doesn't seem to be appropriate here.) I see now, "someone was dead at the age of XX" is an expression one can find in newspaper/novels. Thanks for pointing out :D

Good question! Remember the journalistic style. When newspapers report the news they attempt to be impartial and non-interpretive. To this end, they use several patterns of speech which are not normally used by regular people in daily conversation. Answer B is an example of one of these patterns. Instead of using a verb, an adjective is used which is easily converted into a headline. King Alexander of Macedonia was dead at 32. --> "Dead at 32". I hope this helps :)