Carol is having a hard time attracting hummingbirds to her new feeder location. She is not sure if the reason is that the hummingbirds have a smaller population right now or they just don't like the new food. She has bought some of the old food and wants to test whether that will make a difference.
Identify

She should hang up a feeder of the old food next to the feeder of new food to test which one they really like more.

explanation:

on disadvantage of hydroelectric power is the cost. another disadvantage of using hydroelectric power is finding a water source powerful enough to harvest hydroelectric power.

that would be called plucking : )

explanation:

''plucking, also referred to as quarrying, is a glacial phenomenon that is responsible for the erosion and transportation of individual pieces of bedrock, especially large "joint blocks". as a glacier moves down a valley, friction causes the basal ice of the glacier to melt and infiltrate joints (cracks) in the bedrock."