The best sample is one that is a systematic sample.

a. convenient.
b. representative of the population.
c. purposefully selected.
d. none of the above.

b.representative of the population.  

Explanation:

           A sample is a collection of small quantity or part which is normally taken from a large mass of quantity that represents the whole having the same characteristics.

          A sample should be a representative of the entire population in consideration to make sure to generalize the results from the sample of the research to the population as a whole. A sample is a subset of the population and is considered as the best sample when it represents the whole population.

Hence the correct option is (b).

most cajuns resided in acadiana, where their descendants are still predominant

the correct answer is d