Sentence 1 has a restrictive clause whereas sentences 2 and 3 have nonrestrictive clauses.
What is a restrictive clause?
A restrictive clause restricts or establishes the meaning of a sentence. It is added to a sentence without commas and it is essential for conveying the meaning of the sentence completely.
In sentence 1, “that I left” is a restrictive clause as it specifies which book is on the table.
What is a nonrestrictive clause?
A nonrestrictive clause is used to add specific information to the sentence. It is placed within commas and coveys the same meaning even if the clause is removed.
In sentences 2 and 3, the phrase within the commas is the nonrestrictive clauses. The overall meaning of the sentence does not change even if the clause is taken out.
