13. An insect population in an agricultural field is affected by monthly applications of a pesticide, as shown in the graph above. A likely cause of the overall increase in the insect population over time
is
A. an increase in the population of insect predators
B. an increase in average temperature over the summer
C. an increase in soil salinity
D. a decrease in the moisture content of the soil
the survival of increasing numbers of resistant insects
E