Answer:
The contour interval is 15 meters.
Explanation:
A is not correct because if that was the case we would have had much more contour lines, and if the starting point is 15 meters then 5 contour intervals up would have been an elevation of 40 meters, not 90.
B is not correct because is that was the case we wouldn't have had a contour line of 15 meters, as all contour lines would have been tens, like 10, 20, 30, etc.
C is correct because the elevation distance between the contour line of 15 meters and one of 90 meters is 75 meters, and if we divided that by five (the number of contour lines from one to another marking) we get a value of 15 meters.
D is not correct because just as with the interval of 10, there wouldn't have been a contour line 15, but they would have been 20, 40, 60, etc.
