why not use past tense in the following sentence? my text book says"I asked Sue what happened but she won't tell me" I feel this sentence is wrong. why not say"I asked Sue What happened but she wouldn't tell me"

I'm very confused about the following sentences. my book says"use the present continuous to say what you have arranged to do". But it gives me a example like this: I don't know what I'm doing this evening. Why use present continous here, the person hasn't arranged to do anything.Why not just say"I don't know what I will do this evening"

am I right about the following sentences? If somebody ask me "did you use to go to theatre?". It means she/he knows I rarely go to theatre now, right?

What's wrong with the following sentences. 1)Kevin wrote to Sally many times. She never replied to his letters. Yesterday he had a phone call from her. He was very surprised. (2)Yesterday Kevin had a phone call from Sally. He was very surprised. He had wrriten to Sally many times but she had never replied to his letters. The first and second paragragh are both right(because they are written in my grammar book). But I'm confused why the order of the sentences would change the tense. And I can just understand the second paragraph. Why is the first paragraph right?

What's the difference between these two sentences? my textbook says"John and I went for a walk. I had difficulty keeping up with him because he was walking so fast". Why not say"John and I went for a walk. I had difficulty keeping up with him because he walked so fast". Thanks a lot~

my grandfather died 30 years ago. I never met him why not say 'my grandfather died 30 years ago. I have never met him' thanks for your help!

I've been swimming a lot recently. Why not say 'I've swimmed a lot recently'. thanks for your help~

I'm confusing about past simple and present simple my book says 'we use the present simple to talk about something is true in general'. So why not say: 'Mozart is an Austrian musician and comoposer' instead of 'Mozart was an Austrian musician and composer'

what is 'happenings'? my text book says 'We use present continous tense only for action and happenings'. I know 'eat' is action but what is happening?