In each of the research situations described below, determine whether the researcher is conducting an experiment or a survey.

a. Traps are set out in a grain field to determine whether rabbits or raccoons are the more frequently found pests.

b. A graduate student in English literature uses random 500-word passages from the writings of Shakespeare and Marlowe to determine which author uses the conditional tense more frequently.

c. A random sample of hens is divided into 2 groups at random. The first group is given minute quantities of an insecticide containing an organic phosphorus compound; the second group acts as a control group. The average difference in eggshell thickness between the 2 groups is then determined.

d. To determine whether honeybees have a color preference in flowers, an apiarist mixes a sugar-and-water solution and puts equal amounts in 2 equal-sized sets of vials of different colors. Bees are introduced into a cage containing the vials, and the frequency with which bees visit vials of each color is recorded.