Question

which of the following is true of sinuses? they decrease the surface area for gas exchange. they make the skull stronger. the sinuses have no known function. they produce mucus and clean the air. they dry the incoming air to a comfortable temperature.

Explanation:

The sinuses lighten the skull. They also produce mucus which helps to moisten and clean the air we breathe. They do not decrease gas - exchange surface area, have a known function, do not make the skull stronger in the sense of structural reinforcement, and do not dry incoming air to a comfortable temperature.

Answer:

They produce mucus and clean the air.