Twenty Dogs and 20 Cats Were Subjects in an Experiment

Twenty dogs and 20 cats were subjects in an experiment to test the effectiveness of a new flea
Control chemical. Ten of the dogs were randomly assigned to an experimental group that wore a
Collar containing the chemical, while the others wore a similar collar without the chemical. The
Same was done with the cats. After 30 days veterinarians were asked to inspect the animals for fleas
And evidence of flea bites. This experiment is…

A) randomized block, blocked by type of collar
B) randomized block, blocked by species
C) completely randomized with one factor: the type of collar
D) completely randomized with one factor: the species of animal
E) completely randomized with two factors