Which sentence corrects the vague pronoun in the underlined sentence?

Becca bought a new book as a gift for her friend Ali's birthday. She thought it was the best book she'd ever read, and she bought a copy for another friend.

A. She thought it was the best book they'd ever read, and she bought
a copy for another friend.

B. They thought it was the best book she'd ever read, and she bought
a copy for another friend.

C. Becca and Ali thought it was the best book she'd ever read, and
she bought a copy for another friend.

D. Ali thought it was the best book she'd ever read, and she bought a copy for another friend.
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