根据句意,或汉语提示，写出各单词的正确形式，每空填一词。
These young people are all the _________ (先锋) in this new field.
The ___________(决定) you have made don’t seem so good. You need to be more thoughtful.
The scientists have ____________ (发现) a new way to solve the problem.
Knowing how to use ____________ (字典) will be of great help to learning English.
He _______ (怀疑) if he would learn anything new from Marie when he was at school.