The correct option is D
Height of a rectangular bars represents the frequency of the respective category.
Consider the following example: Hannah collected the data of the type of birds that came into her garden for 20 minutes duration.
Frequency table of the collected data:
Type of Birds
Here the categories are Robin, Dove and Sparrow, i.e., 3 categories.
The bar graph representation is as follows:
There are 3 rectangular bars, one bar corresponding to each category of birds.
Hence, option (b) is correct.
Also, the height of each bar represents the number of birds (frequency) for the respective category.
Number of robins =3
Height of bar corresponding to 'Robin' is 3.
Option (d) is also correct.