【单选题】
Nobody knows how long and how seriously the shakiness（不稳定） of big businesses will （） down the economy.
A、put
B、settle
C、drag
D、knock
查看正确答案
A、A. As an officer on duty, you must know how to adjust derricks. B、B. As a sailor on duty, you must know how to adjust derricks. C、C. As a sailor on duty, you must know how to operate cranes. D、D. As an officer on duty, you must know how to operate cranes.
