A brand of popcorn instructs users to microwave for 90–120 seconds on high. A student wonders what the ideal microwave time for popcorn might be and designs an experiment to find out. Bags of popcorn are placed in the microwave for different lengths of time: 90 seconds, 100 seconds, 110 seconds, and 120 seconds. Also, 2 types of microwaves with different power capacity will be used: 900 watts and 1,000 watts. At the end of the experiment, the number of unpopped kernels will be counted. Using 3 lengths of time and 2 types of microwaves describes which part of the experiment?

the levels

the treatments

the response variable

the experimental units