Oxygen is necessary for combustion.

Hot gaseous products of combustion move upward, causing the influx of more dense cold air to the combustion zone.

Apparently, the officer on duty did not let the bomber to enter the building and the blast burst at the entrance.

We are supposed to take off our shoes at the entrance.

The entrance to the toilet is very dirty.

There is no air on the moon.

There's no air on the moon.

Museum of Ancient Greek Technology, sign at entrance, Katakolon (Peloponnese, Greece).

At the entrance of a Japanese house, visitors are generally asked to take off their shoes.

A police cordon stopped them midway at the bottleneck of Goce Delchev Bridge.

Leaders of self defense groups at the entrance to Churumuco, a municipality in the state of Michoacán.

When the input exceeds a certain threshold, an output signal is instantaneously released.

Taking a glance at the small foyer by the entrance, you can immediately identify the problems that are apparently the most pressing for our home team.

Take off your hat when you enter a classroom.

Take off your hat when you enter a classroom.

Arial view of Tbilisi, Georgia.

Aerial view of Angkor Wat temple

On entering the church premises I was almost broken by the sight of a busload of security forces.

All this, indeed, would be refreshing for Europe.

President Obama's praise of Bwembya was a breath of fresh air for most Zambian citizens.

It would require the state s Air Resources Board to set factory by factory limits on air pollution.

Breath of Fresh Air

An airship is lighter than air.

I went out for a walk to get some fresh air.

Kitty kept looking toward the door, gathering courage not to blush when Constantine Levin should enter.

It composes about 18.2 ppm of air by volume (this is about the same as the molecular or mole fraction), and a smaller fraction in Earth's crust.

Simple solutions can make a vast difference to temperatures.

An aerial view of Guiuan, East Samar.

Aerial view of Maekelawi detention center in Addis Ababa.

Since there is no air on the moon, there is no sound at all.

To live without air is impossible.

Without air, nothing could live.

There is no air in space.

The picture was taken from the air.

Let in some fresh air.

Let some fresh air in.

Tom wanted some fresh air.

Let some fresh air in.

Measured against the relative decrease in air pollution from the reduced fossil fuel energy production, candles increase health damaging air pollution 1,000 10,000 fold.

Spain, for example, was not running a fiscal deficit coming into the crisis.

Last summer I went to Xiamen University where I spent over 10 minutes verifying my ID card to enter, but I understand and support the measure. But cultural scholar Yang Zao s article echoed Jia s view It is indeed a shame for a university that daily tourists are being restricted while touts are saying, Give me 20 yuan, I will bring you into the university.

Attacks from the air on IS forces are necessary but insufficient.

Studies have already established the negative effect of air pollution on health.

An aerial view of contemporary Yerevan.(Image credit Bing Maps).

Another contributing factor to Japan's hay fever problem is air pollution.