Which sentence contains reciprocal pronoun

Rashid and Derek sent each other many e-mails over the summer.

Explanation:

There are only two reciprocal pronouns: "each other" and "one another". In the other two sentences they are either not used or misused. In the sentence: "Alexa asked one another for more information about the class.", "one another" is misused, as it is used in the context of a singular subject. In the other sentence: "The four girls bought themselves sandwiches and drinks.", there is no reciprocal pronoun.

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