Which of the following statements correctly distinguishes a histogram from a bar graph?
(a) A histogram is used for categorical data, while a bar graph is used for continuous data
(b) In a histogram the area of each bar represents frequency, whereas in a bar graph the height alone represents frequency
(c) Both graphs display gaps between adjacent bars to separate classes
(d) In a histogram only the height of each bar represents frequency, whereas in a bar graph the area does