It must never be used in the presence of oxygen at temperatures above 260 C.

The presence of oxygen alone, however, is not conclusive evidence for life.

So, the mere presence of oxygen is not enough; it has to be in a form we can use.

They are very sensitive to the presence of oxygen even at trace level.

This may occur with or without the presence of oxygen.

In the presence of oxygen the color changes quickly.

This process must be done in the presence of oxygen.

Some gases burn in the presence of oxygen, others do not.

In the presence of oxygen, their metabolism is just like ours.

However, this can occur only in the presence of oxygen.