Correct Answer:
B. have
This question tests subject-verb agreement, a fundamental concept in English grammar. The verb must agree in number with its subject. In the second clause of the sentence, "seven resigned," the subject is "seven" (implying seven people), which is plural. Therefore, the auxiliary verb used to complete the present perfect tense must also be plural.
- have: This is the correct choice. "Have" is the plural auxiliary verb used with plural subjects (like "seven") to form the present perfect tense.
- has: This is a singular auxiliary verb and would be incorrect with the plural subject "seven."
- was: This is a singular past tense verb. It is incorrect because the sentence implies a present perfect tense (parallel to "have joined") and the subject is plural.
- is: This is a singular present tense verb and is grammatically incorrect for both the plural subject and the required tense.
Therefore, "have" correctly completes the sentence, maintaining subject-verb agreement and tense consistency.