Question

1. the spread of the flu was lessened by which medical breakthrough?

vaccines
closures
quarantines
antibiotics

Explanation:

Vaccines are medical breakthroughs that help the body develop immunity against specific diseases like the flu. Closures (like closing schools or businesses) and quarantines are non - medical public health measures. Antibiotics are used to treat bacterial infections, and the flu is a viral infection.

Answer:

vaccines