One of the foci for the moon's orbit would be the
(1) sun (3) mars
(2) earth (4) venus

2) Earth

Explanation:

As per Kepler's first law we know that all planets and all satellites revolves in elliptical path with one of its focii as Sun or planet around which satellite and planets are revolving.

Now here we need to know about the focii of moon which is revolving around Earth in its elliptical path.

So as per same law we can say that since moon is revolving around the Earth so its focii must be Earth

So here correct answer would be

2) Earth

the motion of a pendulum is a classic example of mechanical energy conservation. a pendulum consists of a mass (known as a bob ) attached by a string to a pivot point. as the pendulum moves it sweeps out a circular arc, moving back and forth in a periodic fashion.