_____ of economic cycles been helpful in predicting turning points in cycles, they would have been used more consistently.
A. Psychological theories
B. Psychological theories have
C. Had psychological theories
D. Psychologists have theories

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Grammar › ViewHis father taught him how to play the guitar at the ………. of 12.
A. grade
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I took my only son to the park but he didn’t like it. – You ______ him to the zoo.
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What is th outermost layer of the Sun’s atomsphere, located above the chromosphere?
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