Which lines in this excerpt from thomas hardy's "the darkling thrush" signify hope in the midst of despair?

I think you forgot to add some details in this question but based on my research, the correct answer would be:
"At once a voice arose among The bleak twigs overhead 
In a full-hearted evensong 
Of joy illimited; 
An aged thrush, frail, gaunt, and small, 
In blast-beruffled plume, 
Had chosen thus to fling his soul 
Upon the growing gloom."

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"to gaurd against " is correct answer