The heights (in cm) of a set of plants have been grouped as follows:
40–49 : 4
50–59 : 9
60–69 : 12
70–79 : 5
If the horizontal axis of the histogram is drawn with the scale 1 cm = 5 cm of plant height, what will be the length of the base of each rectangle?
(a) 1.8 cm
(b) 1 cm
(c) 2 cm
(d) 5 cm