A histogram shows the ages (in years) of 40 trees in a botanical garden. The class intervals 0–5, 5–10, 10–15, and 15–20 all have equal width of 5 years. The heights of the bars are 4cm, 10cm, 14cm, and 12cm respectively. Which age group is the modal class?
(a) 10–15 years
(b) 15–20 years
(c) 5–10 years
(d) 10–20 years