The nucleus. If a cell has a nucleus it is eukaryotic if it doesn't, it is prokaryotic.
Answer:
A: Cumulative recorder
Explanation:
B. F. Skinner was a psychologist, author, behaviorist and inventor of Operant conditioning chamber and Cumulative recorder. The purpose of cumulative recorder was to study the rate of operant conditioning. It is a process in which behavior of an organism is modified or an organism is conditioned to perform a specific behavior through giving punishment or reward.
For example: We teach a kid that he should not touch a hot stove because it will burn his hands, or we give him a box of candies to perform a specific task or behave in a certain way. Skinner used Cumulative recorder to find the effect of certain factors on behavior or response of an organism For example: the rate at which lever was pressed by a monkey to get bananas etc.
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