#### Answer

a)Discrete.
b)Ratio.
c)Stratified.
d)Cluster.
e)Biased.

#### Work Step by Step

a) The number of stores is always a whole number, therefore it is discrete.
b) We can have an absolute zero (e.g. for 2007) and compare results to this, therefore the answer is ratio.
c) Every store's customers might have different opinions and then selecting from the different stores gives us a good sample. Hence the answer is stratified.
d) Every store can be its own cluster and have a sample that is representative. Hence the answer is cluster.
e) This is a biased voluntary sample, because customers having a really strong opinion (either good or bad) are the most likely to answer, hence the results don't represent the general opinion correctly.