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.