1.What does the professor mainly discuss?
A. Methods of converting radio waves into sound waves
B. Features of different types of electromagnetic radiation
C. The various paths that very-low-frequency waves follow on Earth
D. The emission and detection of very-low-frequency waves
2.What is one difference between radio waves and sound waves that the professor emphasizes?
A. Radio waves have a lower frequency.
B. Water stops radio waves from spreading but does not stop sound waves
C. Unlike sound waves, radio waves can travel outside Earth’s atmosphere.
D. Naturally occurring radio waves are difficult to detect on Earth at night.
3.What explanation does the professor give for the constant occurrence of VLF emissions on Earth?
A. At any given time, some part of the world is experiencing sunrise or sunset.
B. Waveguides constantly form in the atmosphere.
C. Earth’s magnetosphere directs interplanetary waves toward Earth’s surface.
D. Lightning occurs constantly on the planet.
4.Why are sunrise and sunset the best times to listen to VLF signals?
A. Because thunderstorms are most likely to occur then
B. Because radio waves travel through natural waveguides then
C. Because higher-frequency signals are less active then
D. Because temperatures are not extremely high or low then
5.Why does the professor discuss whistlers and tweeks?
A. To illustrate that the path a VLF wave travels can affect the sound it makes on a radio
B. To point out that VLF waves can affect the sounds heard on a household or car radio
C. To describe how a colleague discovered the origin of VLF waves
D. To clarify the difference between VLF waves and other kinds of waves
6.What does the professor imply when he says this:
A. He needs to think before he can answer the woman’s question.
B. The woman has underestimated how often VLF waves can be detected.
C. The woman does not realize that waiting for a thunderstorm can take a long time.
D. The woman does not understand the relationship between thunderstorms and lightning.