The Big Bang occurred
a. about 15 to 20 billion years ago.
b. about 5 to 7 thousand years ago.
c. about 4 to 6 billion years ago.
d. infinitely far in the past.
a
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The synodic period of the moon
a. is about 27.32 days long. b. is the period of time for the moon to orbit Earth once with respect to the stars. c. is the period of time between successive eclipses at a given location on Earth. d. is the period of time from when the moon rises until the moon rises again the next night. e. none of the above
Addition by 1. Components: The figure shows four vectors, 
, 
, 
, and 
, having magnitudes 10.0 m, 8.00 m, 6.00 m, and 2.00 m, respectively. Find the magnitude of the sum of these four vectors.
Fill in the blank(s) with the appropriate word(s).
Suppose we looked at this image without its overlay of radio emission (that is, we looked only at the visible-light image). What features of the image would no longer be visible? Select all that apply.
A) the background galaxies B) the central galaxy C) the jets D) the lobes
Which of the following gases is a trace natural constituent of the air?
a. CO b. SO2 c. CO2 d. NO2