I think its A.
Sorry if it isn't.
Answer:
<u>c. Laboratory experiments have a high degree of control and may create an artificial atmosphere.</u>
Explanation:
A limitation of laboratory experiments is that the environment in which the experiments take place, is very much calculated and controled. This means that it is artificial, and this wll affect the generalization of the findings considering a not cotroling environment such as a real environment.
Please could you indicate what changes are there discussed by the text
I'm pretty sure it's Philadelphia and Denver
Hundreds of slaves. Is says it right there!!!