Which of these periodic motions are simple harmonic ?

A. A child swinging on a playground
B. A record rotating on a turntable
C. An oscillating clock pendulum
D. None of the above

Scientists follow specific processes in order to determine valid explanations and conclusions from observations. david observed strange lights in the sky above his home outside of roswell, new mexico. the only explanation that makes sense to him is that there are ufos in the area. what should david do next to verify his explanation?