The most important measure of the size of a river is the
a. number of its tributaries.
b. width of its mouth.
c. size of its watershed.
d. volume of its discharge.

Hello There! ^_^

Your question: The most important measure of the size of a river is the..?

Your  The most important measure of the size of a river is the volume of its discharge.

The answer is option D.
Happy Studying!

The answer is c, i, iii, and iv. this is because farming and mining deal with harvesting raw materials, construction work falls under manufacturing, and piloting a plane is a service. ii is wrong because making bread is using  raw materials to produce goods, which would fall under the secondary sector, not primary.