Question

cocoa plant type 1 yielded 155 bushels per acre last year at a research farm. this year, cocoa plant type 2, planted in the same location, yielded only 123 bushels per acre and there was a major freeze. the researchers do not know whether the difference is the result of the superiority of type 1 or the freeze. what is this an example of? bias confounding variable matched - pairs design the placebo effect replication

Explanation:

A confounding variable is an outside influence that changes the effect of a dependent and independent variable. Here, the researchers can't tell if the yield difference is due to plant - type superiority or the freeze. The freeze is a confounding variable as it could be influencing the yield results along with the plant type.

Answer:

B. Confounding variable