The total amount of water on earth
a.
is increasing.
b.
is fairly constant.
c.
is decreasing.
d.
depends on the weather.

in theory, limestone is composed principally of the compound calcium carbonate - caco3, but in reality this compound is deposited in conditions involving a number of other compounds as impurities so it ends up being a mixture of many compounds.

hope this : -)

tony (lordcaos066)

im pretty sure its b