The graph shows the fall in cases of tuberculosis (TB) in a country between 1910 and 2000.
Which factors could have contributed to the fall over this period?
1) pasteurisation of milk
2) the provision of new housing
3) chemical treatment of sewage
4) identification of contacts of people infected with TB
1, 2 and 4
2 )
2, 3 and 4
3 )
1 and 3 only
4 )
1 and 4 only
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