Puberty begins with
A. the production of testosterone or estrogen.
B. an increase in the amount of follicle stimulating hormone.
C. the brain sensing the time is right.
D. All of these answers are true.
B. an increase in the amount of follicle stimulating hormone.
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Which of the following are features of guard cells that enable them to function?
A. thick inner walls B. chloroplasts C. cellulose microfibrils D. their shape E. All of these are true
What animal has kidneys that are so efficient that it never has to drink water and can obtain all of its water from its food?
A. camel B. desert lizard C. gerbil D. pocket mouse E. kangaroo rat
Suppose the U.S. Federal Reserve raised its interest rate by 1 percentage point between 2014 and 2015, but the Bank of Canada made no change in its interest rate. You estimate the following model in an attempt to assess the effect of the change in interest rate on the unemployment rate:Unemploymentit = ?0 + ?1U.S.it + ?2Y2015it + ?3U.S.it × Y2015it + UitHere, U.S.it is a dummy variable equaling one if the observation is in the U.S. and Y2015it is a dummy variable equaling one if the observation is in 2015. Which of the following variables may generate an endogeneity problem when attempting to use the estimate for the diff-in-diff (?3) as the effect of the interest rate change?
A. The difference in average labor force participation between U.S. and Canada B. Changes in international immigration laws between 2014 and 2015 C. Changes in overall level of trade in North American between 2014 and 2015 D. Changes in the U.S. fiscal policy between 2014 and 2015
Based on the Luria–Delbrück experiment, mutations that provide plants with the ability to survive on toxic soils should occur:
a. only in populations living on toxic soils. b. in all plant populations. c. randomly. d. A and B. e. B and C.