当管道中流体的雷诺数Re<2000时,则流体的流动状态属于()。
A.层流状态
B.完全紊流状态
C.层流向紊流过渡状态
D.湍流状态
参考答案:A
最早的外科手术器械及用途是:()
A.砭针用于排脓
B.葱管用于导尿
C.铤用于检查治疗漏管
D.用夹板治疗骨折
E.火针用于排脓
— I wonder _ _.
— I'm afraid we'll be late.
A.how we can be on time
B.what we are going to do
C.why we get to school late
D.if we will arrive at the meeting on time