根据所给汉语提示，写出空缺处单词正确形式。

1. _____ (突然) he heard someone crying for help.

2. Yesterday the grandfather bought a _____ (兔子) for his grandson.

3. Mary is going to have a birthday _____ (聚会) next week

4. There is a _____ (洞) on the wall.

5. When he went to the America at first, he felt _____ (陌生的).