29:29'must have', 'might have', 'should have' & 'can't have' to talk about the past: Live English Class
BBC Learning English
Courses on Khan Academy are always 100% free. Start practicing—and saving your progress—now: https://www.khanacademy.org/economics-finance-domain/core-finance/money-and-banking/bitcoin/v/bitcoin-proof-of-work An explanation of cryptographic proof-of-work protocols, which are used in various cryptographic applications and in bitcoin mining. More free lessons at: http://www.khanacademy.org/video?v=9V1bipPkCTU Video by Zulfikar Ramzan. Zulfikar Ramzan is a world-leading expert in computer security and cryptography and is currently the Chief Scientist at Sourcefire. He received his Ph.D. in computer science from MIT.
Published 2013-05-02 · Watch on YouTube ↗
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29:29BBC Learning English
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