Assume that a drop in parasite abundance reflects an effective immune response by the host. explain the pattern you described in question 2.

This question is unfortunately incomplete. This question relates to the advantage derived by some parasites by maintaining a low level of infection in the host. These parasites achieve this by a gene for its surface glycoproteins that is duplicated thousands of times, with each gene coding for a slightly different glycoprotein structure. By constantly shifting between glycoproteins of different structures, the parasite can fool the host into temporarily reversing the immune response. The question includes a table showing the change in parasite blood concentration with time, with the table showing distinct waves of increases in parasite concentration followed by decreases. Using the hypothesis about changing glycoprotein structure, it makes sense that the host begins an immune response, leading to a decrease in parasite numbers, at which point the parasite changes the structure of its surface glycoproteins, thereby allowing the parasite to overcome the immune response, and the concentrations of parasites increase once again. 

The answer is a because - is an direction