1. What USA city cancelled flights because it was too hot?

A. Los Angeles
B. Pittsburgh
C. Phoenix
D. Houston

2. The temperature was above 120 Fahrenheit. That is about ___ Celsius?

A. 0
B. 32
C. 40
D. 50

3. What is the force that pushes up on an airplane's wings called?

A. density
B. lift
C. temperature
D. heat

4. Warm air provides less lift than cold air because it is ____ dense than cold air.

A. less
B. more
C. as dense as

5. Runways are usually longer at high altitudes (in the mountains) because the air is _____.

A. less dense
B. more dense
C. colder
D. warmer

6. What does density measure?

A. It measures how heavy molecules are.
B. It measures how hot molecules are.
C. It measures how far apart molecules are.
D. It measures how friendly molecules are.