1．Don't use water to put out the fire if oil catches fire. As is known, oil ________ float on water.
A．shall B．must
C．may D．will
答案与解析：D will用于陈述真理性的事实，意为“常常会，总是”。句意：当油着火的时候不要用水来灭火。众所周知，油会浮在水面上。
2．—Did your mother sleep well last night?
—She ________ have slept through all those noises.
A．mustn't B．may not
C．can't D．won't
答案与解析：C 根据信息词all those noises可知，她不可能在那种吵闹的环境里睡好觉。对过去动作的推测表示“不可能做某事”应用couldn't/can't have done。
