“lighter than air”造句，怎麼用lighter than air造句

An unmanned free balloon shall refer to a freely drifting inflatable object which is driven with no power, is piloted by nobody, is lighter than air, and whose gross mass is more than 4 kilograms.

What thing is lighter than air that any person can hold in a second or in a minute but never in an hour?

Coral grubbs give off a gas that is lighter than air. This keeps the isles suspended in the sky, but can be a nuisance when attempting to construct buildings.