Earth science EXperts!! Help me out?

during the equinoxes the sun is overhead at the equator, those dates are March 21 and September 23.

During the winter solstice at December 21 the sun is overhead at the Tropic of Capricorn, and on the summer solstice on June 21 the sun is overhead at the Tropic of Cancer. So one February 21 the sun is over head somewhere between the Tropic of Capricorn and the equator moving north but closer to the Equator. (E)

Now for your other question.

Its a matter of perspective. Imagine your riding a merry-go-round and theres a clown just standing by the ride and not moving. But because the merry-go-round your on is spinning the clown seems to move when he is still, same principle with the earth. As your spinning your horse goes up and down so outside objects appear to do the same. Still same principle.

The sun appears to have different positions everyday because earths axis rotaiton is tilted at a 23 degree angle. The angle is fixed for the most part but Earth is orbiting the sun so the sun appears to rise earlier and set later further to the north until the summer solstice then its the opposite as the winter solstice approaches.

The sun doesn't move. Actually the varying position of the sun is due to the fact that our planet is angled by about 23 degrees (this is actually the reason why we have seasons too).

During the winter months (February included in that) the northern hemisphere is faced slightly away from the sun (that's why it's cold, make sense?). This means that at noon the sun is going to be overhead in the southern hemisphere. Since the Tropic of Capricorn is the south bound of the sun, we can tell it has to be either B or E.

February 21 is late winter, so it's already reached the southernmost point, and now it's heading back towards the equator. Therefore, heading northwards. E. Voila.

The sun doesn't move. Earth does, making the sun appear to move across the sky.