根据句意和首字母提示完成句中所缺单词。

1. We are good friends. I think the f_____ between us will be on forever(永远)

2. He is very t_____, please give him a glass of water quickly.

3. There are many d_____ between English and Chinese, but we can learn them well.

4. Don't f_____ to finish your homework on time. Remember that!

5. Forty and fifty is n_____.

和内存储器，外存储器相比的特点是容量小、速度快、成本高。