Sentences with reduced clauses

It is possible in English for a clause to appear in a complete form or in a reduced form.

My friend should be on the train WHICH IS arriving at the station now.

Although IT WAS not really difficult, the exam took a lot of time.

The first sentence shows and adjective clause in its complete form, which is arriving at the station now, and in its reduced form, although it was not really difficult, and its reduced form, although not really difficult.
The two types of clauses that can reduce in English are: (1) adjective clauses and (2) adverb clauses. It is important to become familiar with these reduced clauses because they appear frequently on the TOEFL test.