and, but, because

My friend plays tennis (a)   football.

He walked quickly and slipped on the rock (a)   he didn't get hurt.

I was absent (a)   I had something important to do.

I ran fast (a)   pulled the string of my kite.

The boy was poor (a)   he was happy.

The dress was not that beautiful (a)   it was expensive.

She is clever (a)   beautiful.

I passed the test (a)   I studied hard.

Cycling is good (a)   I don't have a bike.

It is very hot (a)   sunny today.