Contamination occurred during the chemistry experiment.

In this chemical reaction, there is a possibility of contamination.

It is difficult to predict the occurrence of earthquakes.

When the earthquake occurred, we evacuated immediately.

He is majoring in chemistry at university.

We conducted a new experiment in science class.

We will conduct a new chemistry experiment tomorrow.

He is an expert in chemistry.

My keys are inside the house.

He is quite a good cook.