Michael and his sister are / have a lot in common. I've been trying to keep in touch / get in touch with Angela all day.
I have known / met John in 1998.
I think you'll like David when you get to know / get on well with him
We had lost / kept in touch with each other but met again throug
united.​

Michael and his sister are a lot in common.

In this sentence, we need to choose between "are" and "have". The correct answer is "have" because the phrase "a lot in common" indicates that they share common interests or characteristics. So, we would say "Michael and his sister have a lot in common."

I've been trying to keep in touch with Angela all day.

In this sentence, we need to choose between "keep in touch" and "get in touch". The correct answer is "keep in touch" because it means to stay connected or maintain communication with someone. "Get in touch" means to establish communication with someone for the first time. Since the sentence mentions that the action has been happening throughout the day, it implies that the speaker is trying to maintain communication with Angela. So, we would say "I've been trying to keep in touch with Angela all day."

I have known John in 1998.

In this sentence, we need to choose between "have known" and "met". The correct answer is "met" because it refers to a specific moment of meeting someone. "Have known" is used for indicating familiarity or that you knew someone for a period of time. So, we would say "I met John in 1998."

I think you'll like David when you get to know / get on well with him.

In this sentence, we need to choose between "get to know" and "get on well with". The correct answer is "get to know" because it means to become familiar with someone or develop a deeper understanding of them. "Get on well with" means to have a good relationship or compatibility with someone. The sentence mentions that the speaker believes the listener will like David after getting to know him, indicating that the focus is on becoming familiar with David. So, we would say "I think you'll like David when you get to know him."

We had lost / kept in touch with each other but met again through united.

In this sentence, we need to choose between "lost" and "kept in touch". The correct answer is "lost" because it means to become disconnected or separated from someone. "Kept in touch" means to maintain communication or contact with someone. Since the sentence mentions that they met again, it implies that they had become disconnected from each other previously. So, we would say "We had lost touch with each other but met again through united."