I think it is b because there are key word s like ought
Answer:
These atoms will decay as the rock ages, and by measuring the ratio of radioactive isotopes within the rock, scientists can figure out how long it has been around. In 1913, geologist Arthur Holmes published “the Age of the Earth,” the first major effort to date the planet using radiometric dating.
It was a secret diplomatic communication that Germany and Mexico used to form an alliance.
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