Read this sentence._____ Americans had known that yellow fever was spread by mosquitoes, the epidemic of 1793 may have been avoided.Which transition word best connects the ideas?

“If” introduces a condition: Americans’ knowing that mosquitoes spread yellow fever could have led to avoiding the epidemic. The sentence reads, “If Americans had known that yellow fever was spread by mosquitoes, the epidemic of 1793 may have been avoided.” “Because” would give a reason rather than a condition, while “But” and “Then” do not connect the ideas in the intended way.

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