Extra Exam
Question: E3B10

Question: What is the cause of gray-line propagation?

1. At midday, the sun, being directly overhead, superheats the ionosphere causing increased refraction of radio waves
2. At twilight, solar absorption drops greatly, while atmospheric ionization is not weakened enough to reduce the MUF
3. At darkness, solar absorption drops greatly, while atmospheric ionization remains steady
4. At mid afternoon, the sun heats the ionosphere, increasing radio wave refraction and the MUF

Correct Answer: B

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