A pesticide manufacturer is developing a new type of organic pesticide for a particular plant. To study the effectiveness of the new pesticide, a large sample of young plants is collected. The sample is then separated into many groups of two plants based upon age, size and soil type so that plants with similar characteristics are grouped together. One of the two plants in each group is randomly chosen and administered the pesticide, while both plants are placed in a controlled environment and are exposed to the possibility of attack from the target pests. The plants are inspected regularly over a 3 month period and the results are recorded for comparison. This scenario is best described as an example of:
a. anecdotal evidence
b. an observational study
c. a completely randomized design experiment
d. a randomized block design experiment
e. available data
f. a matched pairs experiment