The fish in a particular lake are much larger than the fish in other nearby lakes. bill proposes an idea to explain this, and sally does as well however, their ideas are very different. this means that
a) both ideas are valid
b) neither idea is valid
c) both ideas may or may not be valid
d) depending on the actual situation in the lake, only one or the other idea will be valid

The answer is c because we need to know what did they propose as an answer. the possibility both may be wrong or right. answers a b you can cross out. 

answer: carbon 14 can only be used to determine the age of the organisms that were once living, and igneous rocks are non living.

explanation:

carbon 14 dating is used to determine the age of the sample by estimating the amount of carbon 14 present in the sample and then comparing it with a reference standard.carbon 14 is a isotope of carbon which is radioactive and unstable. carbon 14 is assimilated by all plants and animals throughout their life from carbon dioxide. however, one the organisms die they stop this assimilation and the carbon 14 content starts to decrease.by knowing how much of carbon 14 is left in an organism after his death, one can estimate the age of the organism. the materials whose age can be estimated by carbon 14 method are the organic compounds. however, some inorganic compounds such as aragonite   shell can also be dated.however, if we consider the igneous rocks it is a non living component which never accumulated carbon 14 in it and thus, we cannot use carbon 14 dating method to estimate its age.