用括号中所给单词的适当形式填空。

1．Please call me if you have any problems ____________ （work） out．

2．Marie Curie received the Nobel Prize ____________ （two） during her life time．

3．I think it is ____________ （danger） for children to be close to wild animals．

4．The old man has been ____________ （die） since three years ago．

5．I know only one of the ____________ （visit），how about you?