根据句意和括号中所给中文提示，在句中空格处填写上正确的单词（每空填一个单词）。

1．Students should learn more about how to 　 　 （保护） their eyesight.

2．The old man never feels 　 　 （孤独） because we often go to visit him.

3．We are feeling very sad to lose the great 　 　 （科学家），Yuan Longping.

4．It's one of the good table 　 　 （礼仪） in China to ask the old to eat first.

5．The boy entered the room 　 　 （悄悄） in order not to wake up his mother.