The correct answer is: D. The class work is not being submitted regularly by them.
The verb “submit” is transitive, which means it takes a direct object. In this case, the direct object is “classwork.” The subject of the sentence is “they.” The verb “submit” is in the present progressive tense, which is formed with the verb “to be” and the present participle of the main verb. In this case, the present participle of “submit” is “submitting.” The adverb “regularly” modifies the verb “submitting.”
The other options are incorrect because they do not agree with the subject and verb of the sentence. Option A is incorrect because the verb “have” is in the past tense, but the sentence is about something that is happening now. Option B is incorrect because the verb “has” is in the singular form, but the subject of the sentence is plural. Option C is incorrect because the verb “are” is in the plural form, but the subject of the sentence is singular.
In conclusion, the correct answer is: D. The class work is not being submitted regularly by them.