Structure Skill Toefl 4 : Past Participles

Past participles can cause confusion in the Structure section of the TOEFL test because a past participle can be either an adjective or a part of the verb. The past participle is the form of the verb that appears with have or be. It often ends in -ed, but there are also many irregular past participles in English.

The mailman has left a letter in the mailbox. (Left is VERB)

The classes were taught by Professor Smith. (Taught is VERB)

In the first sentence, the past participle left is part of the verb because it is accompanied by has. In the second sentence, the past participle taught is part of the verb because it is accompanied by were.

A past participle is an adjective when it is not accompanied by some form of be or have.

The letter left in the mailbox was for me. (Left is ADJECTIVE)

The classes taught by Professor Smith were very interesting. (Taught is ADJECTIVE)

In the first sentence, left is an adjective rather than a verb because it is not accompanied by a form of be or have (and there is a verb, was, later in the sentence). In the second sentence, taught is an adjective rather than a verb because it is not accompanied by a form of be or have (and there is a verb, were, later in the sentence).

Example:

The bread _____ baked this morning smelled delicious.

(A) has
(B) was
(C) it
(D) just

In this example, if you look only at the first few words of the sentence, it appears that bread is the subject and baked is either a complete verb or a past participle that needs a helping verb. But if you look further in the sentence, you will see the verb smelled. You will then recognize that baked is a participial adjective and is therefore not part of the verb. Answers (A) and (B) are incorrect because baked is an adjective and does not need a helping verb such as has or was. Answer (C) is incorrect because there is no need for the subject it. Answer (D) is the best answer to this question.

Source : http://www.toeflskill.com/2011/01/skill-4-past-participle.html