Answers to Subject-Verb Agreement Exercise:

1. These students are very friendly. 
The plural subject "students" must take a plural verb "are."

2. Peter Max and Susan Stamberg are speaking on campus next semester.  (correct)

3. A friend of my parents comes to vacation with us every summer.
The subject here is "friend," a singular subject, so the verb must end with "s".

4. The sound of the waves makes me feel drowsy. (correct)

5. Jennifer or her sorority sisters are responsible for giving you pledging information.
Because the subjects are separated by "or," the verb agrees with the noun closest.  Since "sorority sisters" is a plural noun, the verb must be "are" rather than "is."

6. Hot fudge or nuts are perfect in sundaes.
This sentence is the same as #5 which has two nouns separated by "or." .  Because "nuts" is closest to  the verb, and it is a plural noun, the verb is changed to "are."

7. My family hopes you will be able to visit us next summer. (correct)

8.  Both Chris and Mark help to register students.
Because the nouns are separated by "and" here, they become plural; therefore, the verb must be changed to "help."