https://www.reuters.com/article/us-crypto-currency-bitcoin/bitcoin-slumps-further-as-china-tightens-crypto-crackdown-idUSKCN2DX0JI >LONDON/NEW YORK/TOKYO (Reuters) -Bitcoin tumbled on Monday to a two-week low on China's expanding crackdown on bitcoin mining, as investors grew more uncertain about the future of the leading cryptocurrency.