A study was made for the number of persons of different age group visited in a library in week which is shown in the histogram. Study the histogram and answer the question given below.​The ratio of the number of persons in the age groups 15 - 20 years and 20 - 25 years together, to the number of persons in the age groups 30 - 35 years and 35 - 40 year together, is:

• A. 13 : 9
• B. 14 : 17
• C. 15 : 19
• D. 14 : 9