The correct answer is C) frequency.
In fact, the frequency is the number of wave crests (or pulses) per seconds. In our problem, the machine that produces the wave pulses two times per second, so this is exactly the frequency of the compression wave.
1. Volcanoes and minor earthquakes
2. Volcanoes, earthquakes and fold mountains.
3. Earthquakes and fold mountains.
4. Magma from volcanoes is filled with nutrients that makes land fertile.
Good luck!
