He took a day off from school because he had a fever.

He has a fever because he caught a cold.

His first birthday was a very special day.

She was very nervous because it was her first time giving birth.

It's better not to respond to his provocation.

It seems like he is deliberately provoking me.

The development of this area has just begun.

We are working hard to develop new software.

His dog is currently in its sexually active period.

He is studying the behavior of animals when they enter the mating season.