Answer:
<em>Once they had mastered the three kinds of Egyptian writing, nineteenth-century scholars had the key to more than three thousand years of Egyptian history.</em>
Explanation:
The cause-and-effect relationship is a type of relationship where one thing or event makes another one happen. The first thing/event is referred to as the cause, and its consequence is the effect.
The excerpt from<em> The Riddle of the Rosetta Stone </em>that shows this relationship is the fourth one: <em>Once they had mastered the three kinds of Egyptian writing, nineteenth-century scholars had the key to more than three thousand years of Egyptian history.</em>
We have two events - the 19th-century scholars mastering the three kinds of Egyptian writing, and them having the key to more than three thousand years of Egyptian history. The former is the cause of the latter: if they didn't master Egyptian writing, they wouldn't know that much about Egyptian history.
Im my opinoin id say both a and d but id go wit d to be safe
