根据句子意思及汉语提示，写出所缺的单词。
1. Oh, I have (忘) my key in the room, we can't open the door.
2. Though he lives alone, he has a lot of friends and doesn't feel (孤独的).
3. Mrs. White smiled (幸福地) when she received a present from her daughter on Mother's Day.
4. As we all have grown up, we should learn to look after (自己).
5. Everybody knows the (重要性) of doing exercises, but few can keep doing it.