1. We (to be) good friends, we (to know) each other for many years. 2. The ground (to be) wet, it (to rain) all night. 3. He (to run) for an hour when suddenly he (to feel) bad. 4. How many times (you / to meet) her before yesterday? 5. We (to drive) for two hours when, all of a sudden, the car (to break) down.

1. We are good friends, we have known each other for many years.

Explanation: The verb "to be" in this sentence is used in the present tense because the state of being good friends is a current and ongoing situation. The verb "to know" is in the present perfect tense because it indicates an action that started in the past (when the friendship began) and continues until the present.

Step-by-step solution: The first part of the sentence is already in the present tense, so we just need to change the verb "to know" to the present perfect tense. We can do this by using the auxiliary verb "have" with the past participle "known". So, the correct sentence is: "We are good friends, we have known each other for many years."

2. The ground is wet, it has been raining all night.

Explanation: The verb "to be" in this sentence is used in the present tense because the state of being wet is a current and ongoing situation. The verb "to rain" is in the present perfect continuous tense because it indicates an action that started in the past (the rain started last night) and continues until the present.

Step-by-step solution: The first part of the sentence is already in the present tense, so we just need to change the verb "to rain" to the present perfect continuous tense. We can do this by using the auxiliary verb "have" with the present participle "been" and the base form of the verb "rain". So, the correct sentence is: "The ground is wet, it has been raining all night."

3. He had been running for an hour when suddenly he felt bad.

Explanation: The verb "to run" is in the past perfect continuous tense because it indicates an action that started and continued in the past until another event happened (he felt bad). The verb "to feel" is in the past simple tense because it indicates a completed action in the past.

Step-by-step solution: The first part of the sentence is already in the past perfect continuous tense, so we just need to change the verb "to feel" to the past simple tense. We can do this by changing the form of the verb to its past simple form "felt". So, the correct sentence is: "He had been running for an hour when suddenly he felt bad."

4. How many times had you met her before yesterday?

Explanation: The verb "to meet" is in the past perfect tense because it indicates an action that happened before another past action (yesterday). The word "before" indicates the time reference.

Step-by-step solution: The given sentence is already in the correct tense, so we don't need to make any changes.

5. We had been driving for two hours when, all of a sudden, the car broke down.

Explanation: The verb "to drive" is in the past perfect continuous tense because it indicates an action that started and continued in the past until another event happened (the car broke down). The verb "to break" is in the past simple tense because it indicates a completed action in the past.

Step-by-step solution: The first part of the sentence is already in the past perfect continuous tense, so we just need to change the verb "to break" to the past simple tense. We can do this by changing the form of the verb to its past simple form "broke". So, the correct sentence is: "We had been driving for two hours when, all of a sudden, the car broke down."