Read these two excerpts from the selection. Together, these excerpts

England's Stonehenge and the pyramids of Old and New Worlds were all designed to track time over thousands of years. They did this by using shadows. In these "clocks," the thing counting time is the Earth itself, going around the Sun once each year. But they no longer keep perfect time today, because the stars used to align them have actually moved in the night sky since they were all built!

Nature also provides ways to measure long periods of time. Tree rings and ice cores let scientists reconstruct weather back thousands of years. Radioactive isotopes decay (turn into simpler elements) at regular markers of time, letting archeologists date the age of ancient ruins, and geologists measure the age of the Earth. (While atomic clocks measure changes in an atom's electrons, radio dating measures changes in an atom's nucleus.) Pulsars are spinning magnetized cores in space. They emit gamma rays at precisely timed pulses. Counting these bursts can help astronomers chart the longest time of all the age of the universe.

A-offer an argument for sticking to just one way to measure time.
B explain how people can measure time that is too fast for the human eye to see.
C provide examples of how people have learned to measure long periods of time.
D suggest that people have only recently learned to measure time.