I think the answer is "In 1867, the United States bought Alaska from Russia for $7 million". When you ask the question "when" the question is asking about time. In this excerpt, when is answered by "in 1987". while the sentence supported it is the event that happened during that time, which is " The US bought Alaska from Russia for $7 million.
3 Stanzas, the stanzas are like paragraphs for poetry
ABCB is the rhyme scheme, hope that's what you where looking for
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