Last class I attended a important meeting. -> Last class, I attended an important meeting.

So I didnt attend my class. -> That's why I didn't attend my class.

So I prepare to study today's class. -> I studied the lesson for this class.

Theseday I am very busy because korean traditional holiday "chooseok"is comming. -> I'm very busy these days because korean traditional holiday "chooseok"is comming.

So I have to visit my clients and give the present. -> I have to visit my clients and give them presents.

But I have exercised swimming because I want to be a lifeguard. -> I also practiced swimming because I want to be a lifeguard.