Many writers make the mistake of disunity in tense. What does this mean?

This means that the tenses do not agree, more like Concord.

Explanation:

Concord in grammar means subject-verb agreement. That is, if a verb is in the singular form, then the subject must be in the singular; and if it is in the plural, then the subject must be in the plural.

When a writer makes a mistake of disunity in tenses, it means that the sentence does not follow the subject-verb rule.

For example,

The group of dancers is here is wrong because the dancers are in plural, but the singular verb is is used.

Correcting the sentence,

The group of dancers are here.

B)Vincent most likely got hired and is nervous to start his new job.

Explanation:

Based on the stage directions, Vincent most likely got hired and is nervous to start his job. The stage directions describe him dressed in a work uniform, sighing before walking into the store, and nervously biting his lip.