I think these are the answers:
A) My father doesn’t like dancing but I like dancing.
B) He failed his exam although he studied hard.
C) I didn’t attend my class yesterday because I was sick.
D) The phone rang while I was taking my online class.
E) We explore the internet so that we can learn many new things.
They are efficient for rare diseases or diseases with a long latency period between exposure and disease manifestation.
I think it's the last one or the third one.
