D) continued into the 2010s
Answer:
<h3>The proposed 26th Amendment passed the House and Senate in the spring of 1971 and was ratified by the states on July 1, 1971.</h3>
The principle of superposition states that the oldest sedimentary rock units are at the bottom, and the youngest are at the top. Based on this, layer C is oldest, followed by B and A. So the full sequence of events is as follows: Layer C formed.