Select the correct answer.

the chart gives the number of cases of pollo between 1937 and 2011. polio is an infectious disease that causes paralysis and sometimes death.
the pollo vaccine was introduced in 1955. what can be concluded about the polio vaccine?
a. it was successful eradicating polio from the united states.
b. it has no effect on the number of polio cases in the united states.
c. it reduced the number of polio cases, but deaths from polio stayed constant.
d. it initially lowered the number of polio cases, but the number of us cases remain high.