Fact 1: Passive immunity lasts only as long as the antibodies survive in body fluids. Fact 2: Breast Milk contains antibodies. Given the two facts above, what can make passive immunity last?

Select from:
1). resistance
2). sweating
3). Leptospirosis
4). breast milk
5). smoking tobacco
6). the environment
7). competition
8). fur seals
Answer:
4).