Final answer:
In a test to determine which of two plastics is more biodegradable, the dependent variable is the amount that the plastics decay, as it is the aspect being measured in response to experimental conditions.
Step-by-step explanation:
When testing to see which of two plastics is more biodegradable, the dependent variable in the experiment could be b) The amount that the plastics decay. This is because the dependent variable is the factor that is being tested or measured in an experiment, which, in this case, is the extent to which each plastic decomposes. The independent variable could be variables such as the duration of the experiment, the type of soil, or other conditions under which the plastics are buried. The results depend on how biodegradable the materials are, rather than their size or the time they are left to degrade.