根据句意，在答题卡标有题号的横线上，写出括号内所给单词的适当形式。
Bill Gates is the ________ (wealth) person in the world on 2015 Forbes list.
The police are worrying about the ________ (safe) of the 12-year-old boy who has been missing for three days.
The advice which he refused to take at first proved ________ (value) in the end.
A huge forest fire ________ (break) out after the lightning hit it.