三. 用括号内所给词的适当形式填空。
1. Sometimes scientists are __________(puzzle) by some unexplained phenomena.
2. The concerned parents and the teachers went into the forest in________(searching) of the missing child.
3. The teachers have ruled out the_________(possible) that he cheated in the examination.
4. To our surprise, the young woman was the__________ (murder) who has killed her parents.
