Why does the poet say “storm-cloud dark”?

The poet said storm cloud dark because the man was sad and the sky was cloudy

Hope that this the right ans

answer: from these honored dead we take increased devotion to that cause for which they gave the last full measure of devotion—that we here highly resolve that these dead shall not have died in vain, that this nation under god shall have a new birth of freedom, and that government of the people

explanation:

i would have to say "a" or "d".