Sentence 1 is an example of. Sentence 1: My friends are planning to spend their summer vacation at the seashore.

a. a sentence fragment.

b. incorrect subject-verb agreement ...

c. a run-on sentence.

d. correct subject-verb agreement.

Sentence 1 is an example of Correct subject verb agreement

Explanation:

The given sentence is in the form of subject verb and agreement the given subject is singular so the verb is also singular this is the basic rules for the subject verb agreement. If the verb agrees upon the subject then it is called as subject verb agreement.

This sentence pattern is employed in many sentences and there are basic set of rules for the usage of these sentences. This is correct pattern of the subject verb and agreement format.