Question

crayfish are freshwater crustaceans. they breathe through feather - like gills and are found in water that does not freeze to the bottom. they are mostly found in brooks and streams where there is fresh water running. most crayfish cannot tolerate polluted water. crayfish feed on living and dead animals and plants. dennis wanted to see if crayfish preferred one kind of food over another. he gave one group of crayfish plants, both living and dead, and gave the other group insects, living and dead, to eat. what is the independent variable? a type of food b weight of crayfish c type of water used d age of the crayfish

Explanation:

In an experiment, the independent variable is what the experimenter manipulates or changes. Here, Dennis is changing the type of food (living and dead insects, plants) given to the crayfish groups to see which type the crayfish prefer. The weight of crayfish, type of water, and age of crayfish are not what he is directly changing to test his hypothesis about food preference.

Answer:

A. type of food