Air is an odorless  , invisible   gas that surrounds the earth. It is everywhere on the planet. An "empty" drinking glass and an "empty" room, to give two examples, are not really empty. Each is filled with air. When the glass is filled with water, the water pushes the air out of the glass. Air, as a gas, has no definite   shape, but, because it is matter, it takes up space. It is easy to prove that air is something that takes up space. _ a dry handkerchief into the bottom  of a glass so that it will not fall out when the glass is turned upside-down. Push the upside-down glass; hold it straight into a jar of water till the glass is completely covered. When the glass is taken out of water, the handkerchief will be dry. The air inside the glass takes up space and keeps the water from coming in. The writer tells us that   _  .
the experiment is done in the laboratory the experiment is done outside the room the experiment is easily done the experiment is carried out indoors