The graph shows the number of new houses built from 1970 to 2000. The mayor used the graph to claim the number built increased at a constant rate.

A) It is valid because the graph shows a constant rate of change.

B) It is valid because 30 years is long enough to evaluate the increase.

C) It is not valid because the scale on the vertical axis is inappropriate.

D) It is not valid because the scale on the horizontal axis is inappropriate.