Which is the FOURTH sentence of the paragraph?

Rearrange the following six sentences a, b, c, d, e and f in the proper sequence to form a meaningful paragraph; then answer the questions given below them.
a) In the early 1970s, nearly 10,000 people a year got it.
b) But the graph of cases in the US over time looks like the second, fun half of a roller coaster ride.
c) By the mid-1980s, the number was half that.
d) Hepatitis A is a viral disease that primarily attacks the liver, and if it gets serious, as it can in the elderly and immune-compromised people, it can be fatal.
e) Then, this past summer, people started getting sick in San Diego. Just a handful at first, among those most at risk.
f) In 1996, the Centers for Disease Control and Prevention started recommending vaccination, and from there it was a fast, bracing plunge to just tens of cases a year.