When a researcher asks the question, "Have subjects been pre-selected so as to represent the extremes on the variable of interest?", she is concerned with which one of the following potential threats to internal validity?

A. Regression effect
B. Subject selection
C. Testing effect
D. Maturation

industry had made the u.s. the richest nation in the world at this time. the second industrial revolution caused growth in industry and transportation, which allowed increased trade between nations.

i believe

clean air is essential for health and survival

clean air provides nitrogen gas for plant respiration

clean air supplies oxygen that enables living organisms to breathe

hope this

i am brianly

sorry if this doesn't

answer; /// the above statement is (false);