Within the atmosphere as the altitude increases?

Within the atmosphere, as altitude increases,

A.air pressure stays the same.

B.air becomes heavier.

C.air pressure decreases.  The answer.

D.air pressure increases.

Explanation:

That's the question. AND Pressure with Height: pressure decreases with increasing altitude. The pressure at any level in the atmosphere may be interpreted as the total weight of the air above a unit area at any elevation. At higher elevations, there are fewer air molecules above a given surface than a similar surface at lower levels. Hope that helps. This means the answer is C.

answers: to make sure that all of the broken pieces of tablet were added to the water, to allow for fair comparison of all three trials, with different particle sizes to avoid experimental error

i do not get it   at all