In Lamberti and Resh's Experiment, What Was the Purpose of Having

Multiple Choice

In Lamberti and Resh's experiment, what was the purpose of having a second grid of tiles raised 15cm above the stream bottom?

A) To prevent algae and bacteria from colonizing the tiles
B) To encourage algae and bacteria to colonize the tiles
C) To prevent Helicopsyche from colonizing the tiles
D) To encourage Helicopsyche to colonize the tiles