Astudent was testing to see if hummingbirds are drawn to the color red. she hung 4 hummingbird feeders in a tree (one red, one blue, one green, one yellow). at the beginning of each day, she filled each feeder with hummingbird food. at the end of each day, she measured how much food the hummingbirds had drank from each feeder. she did this for 7 days. what was the independent variable in her experiment? a) hummingbird feeder size b) hummingbird feeder color c) amount of food the hummingbirds drank d) number of days she did the experiment