The two methods used for determining mass are: measuring directly on a scale measuring directly on a balance measuring directly by displacement of water calculated by measurements of w and g

He's trying to say A and C

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)

wher is the rest of the question