THE SUBJECT OF A SENTENCES MAY BE WHAT PART OF SPEECH
What about nouns and pronouns, including proper nouns?
Here are some excellent websites that will help with basic grammar questions like yours:
http://www.chompchomp.com/menu.htm
Click on TERMS and find what you need.
http://english-zone.com/index.php?ID=1
Lots of good information in various places here.
http://owl.english.purdue.edu/handouts/grammar/index.html
Use the list on the left as the table of contents to find what you need.
http://grammar.ccc.commnet.edu/grammar/
Click on the menu for Word & Sentence Level and then choose whatever grammatical/usage item you need information on.
http://www.uottawa.ca/academic/arts/writcent/hypergrammar/grammar.html
Under the details, click on the area you need information on and go from there.
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