Despite the seemingly ______ nature of the negotiations, the diplomats managed to forge a durable peace agreement, defying all expectations. Which pair of words, when inserted into the blank, best completes the sentence to produce two sentences alike in meaning?

✓ Correct Answer: Option B

The phrase 'defying all expectations' suggests the negotiations were surprisingly successful despite inherent difficulties. 'Intractable' and 'obdurate' both mean difficult to manage, control, or persuade, fitting the challenging context.