Final answer:
The error in the sentence is the verb 'have' which should be 'has' following the singular subject 'each'. 'Each' implies individual reference, necessitating a singular verb for correct subject-verb agreement.
Step-by-step explanation:
The error with subject-verb agreement in the sentence 'Four laptops have been purchased for the new employees. Each have the relevant software, ample memory and storage, and virus protection.' is the use of the verb 'have'. When 'each' is used as a subject, it should be followed by a singular verb because 'each' refers to individual members of a group, one at a time, rather than the group as a whole. Therefore, the correct verb to use is 'has', making the corrected sentence: 'Four laptops have been purchased for the new employees. Each has the relevant software, ample memory and storage, and virus protection.' To ensure proper subject-verb agreement, consider whether the subject is singular or plural, and whether it is a collective noun. Collective nouns can take a singular or plural verb depending on if the group acts as a single unit or individually. Regular proofreading can help writers identify and correct these errors.