The graph illustrates the decrease in cases of tuberculosis (TB) in a country from 1910 to 2000. Which of the following factors may have helped cause this decrease during this time? 1 milk pasteurisation 2 the supply of new housing 3 chemical processing of sewage 4 tracing the contacts of people infected with TB
- A1, 2 and 4
- B2, 3 and 4
- C1 and 3 only
- D1 and 4 only