单选题 Nobody yet knows how long and how seriously the shakiness in the financial system will ______ down the economy.

【正确答案】 C

【答案解析】[解析] 各项的意思是：put down是“放下；降落”；settle down是“定居；平静下来”drag down是“拖垮，拖后腿”；knock down是“击倒，撞倒”。所以，本题选C。