Which of the following is often a main difference between a
coastal plain and an interior plain?
a. elevation
b. relief
c. contour
d. latitude

The answer is
A) elevation

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.