Comma and that/which/who

None of the sentences require commas, and they are all alright.

Jangsunny, the usual placement for this would be,

Are those sentences all right?

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Relative clauses seem difficult because they are usually presented without any context. You can help yourself a great deal in understanding them by practicing your own wherein you provide the context. You can do this with your friends too. Create situations and use objects to formulate and practice relative clauses.

Situation: a paper, term paper, a pencil, any object

['this' combined with a waving action makes the noun/object known, hence an added info clause with pauses/commas]

This pencil, which was given to me by [name], is yellow.

Two or more pencils in varying positions, hence the need for an identifying clause.

The pencil that/which I'm holding is blue.

Some pieces of paper in various states - wrinkled, crumpled, folded, torn, etc.

The paper which/that I dropped was wrinkled by [name].

This one, which was torn by [name], is sitting/situated at the middle left of the table.

There are millions of possible scenarios in which it is possible for you to not only practice in context but practice in actual speech. Nothing is better for actually learning a language and making these "dead grammar" issues come alive. Nothing is better for setting these "dead grammar" issues into your brain. That's what will make you a competent user of the English language.

Thank you so much

Thank you

I'll go over the grammatical issues for relative clauses as soon as I find some time, J.