From where did the molecular oxygen in Earth's atmosphere originate?
A) photosynthesis from plant life
B) photosynthesis from single-celled organisms
C) outgassing from volcanoes
D) atmospheric bombardment
E) oxidation of surface rocks
B
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In brittle materials, the easiest way to increase the _________strength is to decrease the size of cracks and pores.
Fill in the blank(s) with the appropriate word(s).
At sea level, at a latitude where 
, a pendulum that takes 2.00 s for a complete swing back and forth has a length of 0.993 m. What is the value of g in m/s2 at a location where the length of such a pendulum is 0.970 m?
A. 0.098 3 B. 3.05 C. 9.57 D. 10.0 E. 38.3
In a resonating pipe that is open at both ends, there
A) are displacement nodes at each end. B) are displacement antinodes at each end. C) is a displacement node at one end and a displacement antinode at the other end. D) None of the above are possible.
Lightning between a cloud and the surrounding air is called
a. air discharges. b. cloud discharges. c. ground discharges. d. intracloud discharges.