I get the feeling that he's hiding something.

Please be careful when crossing the road.

Please be careful of cars when crossing the road.

His body showed a rejection reaction to the transplanted organ.

His single word triggered a chain reaction, and everything changed.

She overreacted to his words.

Nuclear reactions are used for mass production of energy.

I was surprised by his overreaction.

His way of speaking is affected, lacking in naturalness.

I can't forget the day when I first shared an umbrella with him.