Ukraine: Is Russia losing?

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It's been a week of extraordinary territorial gains by the Ukrainian army. In the north-east of the country near the city of Kharkiv, Ukraine says it's now liberated more than 20 towns and villages. It's also recaptured the strategically important city of Izyum. So how has Ukraine managed to make such sweeping gains, and what's behind the sudden reversal of fortunes? BBC Diplomatic Correspondent Paul Adams has the answers to 5 key questions. Image Credit: Ammar Awad, Reuters