The primary purpose of the excerpt is to explain to children that the moon causes the tides. Thus the correct answer is A.
What is a purpose?
The purpose is referred to the intent or objective of any literature work and why it exists or is created. This purpose helps to increase reach to a wider audience in terms of better understanding.
The excerpt from "The Crab That Played with the Sea.” reflects a setting on the beach side where imagination is used to set the tone. In this excerpt, it is highlighted the explanation of tides caused by the moon to the children is being done.
Therefore, option A to explain to children that the moon causes the tides is the appropriate answer.
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