Recall that during the Paleozoic Era, atmospheric CO2 levels decreased. Why?
A. New, extensive mountain ranges formed
and chemical weathering decreased.
B. Earth's plate tectonics changed
dramatically, and subduction increased.
C. Photosynthetic, woody plants first
appeared during this period.
D. Volcanism decreased during this period.
C
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A cytoskeleton enables eukaryotic cells to:
A. move. B. engulf other cells. C. change shape. D. All of these choices are correct.
Which of the following is (are) among the most
effective contraceptive approaches? a. abstinence b. tubal ligation c. vasectomy d. hormonal implant e. all of these
For the average person in the U.S., the largest source of radiation exposure is
A. background radiation. B. medical X-rays. C. irradiated food. D. consumer products. E. remote-controlled devices.
Which of the following is a key component of the cytoskeleton?
a. centrosome b. microtubules c. DNA d. ribosomes e. endoplasmic reticulum