Chapter 15, Problem 13RA

Active immunity may be produced by

$\begin{array}{l}\text{a}\text{. contracting a disease}\text{.}\hfill \\ \text{b}\text{. receiving a vaccine}\text{.}\hfill \\ \text{c}\text{. receiving gamma globulin injections}\text{.}\hfill \\ \text{d}\text{. bothaandb}\text{.}\hfill \\ \text{e}\text{. both b and c}\text{.}\hfill \end{array}$