Hi Jupiter, Prasoeur and everyone!
Thank you both very much indeed for sharing your good answers here. I hope it will be clearer and clearer for us English learners.
What can be subjects?? I have concluded the answers from your replies above.
1/ NounWater is important for us. (single word)
The members of the website, like Jupiter & Prasoeur, are very active. (phrase)
2/ PronounYou can be my good friends.
Everybody in the class became silent.
3/ GerundSpeaking English every day does help!
4/ Infinitive (with to)[/i][/b]
To prepare for the future is to try hard.
5/ wh-word + to verb (what/when/where/why/how/whose/whom/which...)
What to do is not understood.
How to make friends is not easy. What do you think?
6/ Noun clauseThat you are an important person doesn't bother me.
When we will chat online is not finally decided yet. (what/where/why/when/how/who/whom/which...)
7/ Adjective used as nounThe poor are always suffering under the drunk leaders.
(An adjective used with "the" can become a noun.)
the rich, the poor, the clever,................
Hey, this is what I have learned. We are welcoming any shared ideas from you all!