The nonessential clause is underlined in sentence c) Its coloring, <u>which is brown and green</u>, allows it to hide in marshy areas.
The underlined clause in this sentence is a non-defining relative clause, which only adds information about the noun phrase it modifies. Without the clause, the sentence is still gramatically correct and the meaning of the sentence does not change. Furthermore, non-defining relative clauses have to be written between commas.
The essential clause is underlines in sentence d) The person <u>who sells souvenirs</u> is in the lobby.
The underlined clause in this sentence is a defining relative clause, which gives essential information about the noun phrase it modifies. Without the clause, the meaning of the sentence changes (it is no longer a specific person the sentence is talking about). Furthermore, defining relative clauses are <em>never</em> writteng between commas.
