How long did it take for oxygen to build up in the Earth's atmosphere to its present levels?
A) at least 542 million years
B) at least 360 million years
C) at least 2 billion years
D) at least 3.5 billion years
C
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The end of a compass needle that points to the south pole of a magnet is the
A) north pole. B) south pole. C) both of these
Two uses of ultrasound are __________ and __________
Fill in the blank(s) with correct word
Two ideal Carnot heat engines have the same efficiency. One operates between 5.0 × 102 K and 3.0 × 102 K, and the other between 4.0 × 102 K and some lower temperature. What is the lower temperature?
A) 200 K B) 220 K C) 240 K D) 260 K E) 280 K
A compound microscope has an eyepiece that:
a. uses a real image from the objective as the object and forms a virtual image. b. uses a virtual image from the objective as the object and forms its own virtual image. c. uses a real image from the objective as the object and forms its own real image. d. uses a virtual image from the objective as the object and forms its own real image.