Надеюсь всё понятно))
A: How often do you use Twitter(simple)
B: I read other people's tweets but I don't tweet(simple потому что в вопросе был simple)
A: And what is Twitter good for?
B: Well I'm scientist and I usually use Twitter for my work. It's very important for me to know what happens in my field currently(simple)
A: So who are you follow at the moment?(continuous потому, что at the moment)
B: Right now I am following a conversation between two scientists in Canada about he environment.(continuous во первых now во вторых на вопрос ответ)
А: And what about other subjects?
B: Sometimes I look at what famous people say at the moment about things in the news. This week a lot of people talk about the situation in the Middle East.