Answer: Option D: larger than 1.5 inches, smaller than 6 inches, warts, no triangular mark on head, X-shaped mark on back
Explanation: Pseudacris crucifer is the last species of frog in the key. Therefore, one must work backwards through the entire key to determine Pseudacris crucifer's characteristics.The only way to get to step #5, where the frog was identified as Pseudacris crucifer, was to determine in step #4 that the frog had no triangular mark on its head.To get to step #4, the frog must not have had smooth skin. In order to get to step #3, our frog must have been smaller than 6 inches.Although we could have arrived at step 3 whether the frog was larger or smaller than 1.5 inches, the only answer choice provided that correctly listed the other characteristics of Pseudacris crucifer is : larger than 1.5 inches, smaller than 6 inches, warts, no triangular mark on head, X-shaped mark on back.