english:過去式

Q1: 係 e.g. I was late for school this morning so I was punished by Mr Chan.
Q2: 係, infinitive 有兩種, 分別係 to-infinitive 同 bare infinitive
to-infinitive: e.g. I wanted to go shopping in Causeway Bay. I decided to do my homework myself. (to 後面嘅動詞唔轉)
bare infinitive: e.g. I will help you draw the card. / Let me tell you a story. / I could not believe my eyes. / Tom made me cry yesterday. (某啲字後面嘅動詞唔轉, e.g. let, make, help, can, must, may, will......)

english:過去式是時間有關係-
和conjunction 沒有關係
i ate an apple and it was sour = correct.\
or
I ate an apple, which was sour.
or
I ate a sour apple

Q1. 係,
eg. It was hot yesterday and i went swimming.
I went shopping and I spent some money.
講過去ge事ge時候, 因為conjunction之前同之後一定要吻合. 唔可以唔同tense

Q2. 係,
eg. I have to do my homework
She is going to play the piano
infinitive之後一定不變, 唔可以用其他tense