Option a) is the answer given in the answer key. Can you please explain why is option a) correct and on what basis are we eliminating the other options? Isn't option b) the most appropriate answer?
Here the poet is asking the officials to free the children from the shackles that bind them.Hence , he wants that the children break free from the confined "catacomb" they are caught in.That is why a is correct.
(b) is talking about being bold to break the barrier which is not perfectly in context
(c) and (d) are completely out of context here (you can compare them with the explanation for (a) )