8. An air delivery service company places packages into large containers before fly- ing them across the country. These filled containers vary greatly in their weight. Suppose the company's airplanes always transport two such containers on each flight. The two containers are chosen so their combined weight is close to but does not exceed a specified weight limit. A random sample of flights with these containers is taken, and the weight of each of the two containers on each se- lected flight is recorded. The weight of the two containers on the same flight will have a

a. correlation of 0.

b. negative correlation.

c. correlation of 1.

d. positive correlation less than 1.