Explanation:
The correct answer is option 'A'. Let's understand why.

Present Perfect Continuous Tense:
The sentence is in the present perfect continuous tense. This tense is used to express an action that started in the past, is still happening in the present, and may continue into the future. It is formed using the auxiliary verb "have" in the present tense, followed by "been" and the present participle (-ing form) of the main verb.

Usage of Present Perfect Continuous Tense:
The present perfect continuous tense is used to describe actions or situations that have been happening over a period of time and are still happening at the time of speaking. In this sentence, the action of the phone ringing started in the past when Jack announced his candidacy for mayor and is still happening at the present moment.

Option Analysis:
Let's analyze each option to understand why option 'A' is the correct choice.

a) has been ringing: This is the correct answer. It correctly uses the present perfect continuous tense to show that the phone has been ringing continuously since Jack announced his candidacy for mayor.

b) was ringing: This is incorrect. The past tense "was ringing" suggests that the action of the phone ringing has already finished and is not ongoing.

c) had been ringing: This is incorrect. The past perfect continuous tense "had been ringing" suggests that the action of the phone ringing started and finished before another past event. However, there is no indication of another past event in the sentence.

d) rang: This is incorrect. The simple past tense "rang" suggests that the action of the phone ringing happened at a specific point in the past and is not ongoing.

Conclusion:
The correct answer is option 'A' because it accurately uses the present perfect continuous tense to convey that the phone has been ringing continuously since Jack announced his candidacy for mayor.