A market research company wishes to find out whether SFU students prefer brand A or brand B of instant coffee. A random sample of students is selected, and each one is asked to try brand A first and then brand B (or vice versa, with the order determined at random). They then indicate which brand they prefer.

(a) This is an example of

A.block design.

B.stratified sampling design.

C.a matched-pairs experiment

D.an observational study, not an experiment.