When viewed from earth, mars appears to change colors. this most likely happens because
a. gases in the dense martian atmosphere are constantly changing.
b. volcanic activity produces thick gas clouds.
c. dust storms lasting for weeks cause the atmosphere to change color.
d. active volcanoes on the mars surface intermittently flood the surface with lava.

C. dust storms lasting for weeks cause the atmosphere to change color. 
mars has a relatively thin atmosphere
there is limited to no volcanic activity on mars.

The correct answer is c

An  atom  (ours, not carroll's) consists of a positively charged  nucleus, surrounded by one or more negatively charged particles called  electrons. the positive charges equal the negative charges, so the atom has no overall charge; it is electrically neutral. most of an atom's mass is in its nucleus; the mass of an electron is only 1/1836 the mass of the lightest nucleus, that of hydrogen. although the nucleus is heavy, it is quite small compared with the overall size of an atom. the radius of a typical atom is around 0.1 to 0.25 nanometres (nm), whereas the radius of a nucleus is about 10-6  nm.  *  if an atom were enlarged to the size of the earth, its nucleus would be only 200 feet in diameter and could easily rest inside a small football stadium.read more on -