1) Had you heard the song that somebody sang? 2) Have we been to Mexico before? 3) Had I not seen him for five years?

1) "Had you heard the song that somebody sang?" - the sentence is in the past perfect tense. In this tense, we use the auxiliary verb "had" + the past participle of the main verb. The main verb in this sentence is "heard," which is the past participle of "hear." The subject of the sentence is "you."

To answer this question, we need to know whether "you" had heard the song that somebody sang or not. If the answer is "yes," we can say: "Yes, I had heard the song that somebody sang." If the answer is "no," we can say: "No, I hadn"t heard the song that somebody sang."

2) "Have we been to Mexico before?" - the sentence is in the present perfect tense. In this tense, we use the auxiliary verb "have/has" + the past participle of the main verb. The main verb in this sentence is "been." The subject of the sentence is "we."

To answer this question, we need to know whether "we" have been to Mexico before or not. If the answer is "yes," we can say: "Yes, we have been to Mexico before." If the answer is "no," we can say: "No, we haven"t been to Mexico before."

3) "Had I not seen him for five years?" - the sentence is in the past perfect tense. In this tense, we use the auxiliary verb "had" + the past participle of the main verb. The main verb in this sentence is "seen," which is the past participle of "see." The subject of the sentence is "I."

To answer this question, we need to know whether "I" had not seen him for five years or not. If the answer is "yes," we can say: "Yes, I had not seen him for five years." If the answer is "no," we can say: "No, I had seen him within the past five years."

4) "Did he ever play tennis before yesterday?" - the sentence is in the past simple tense. In this tense, we use the auxiliary verb "did" + the base form of the main verb. The main verb in this sentence is "play." The subject of the sentence is "he."

To answer this question, we need to know whether "he" ever played tennis before yesterday or not. If the answer is "yes," we can say: "Yes, he had played tennis before yesterday." If the answer is "no," we can say: "No, he hadn"t played tennis before yesterday."