层流、紊流的判别标准：临界雷诺数是（）。
A．上临界雷诺数
B．上临界雷诺数和下临界雷诺数的平均值
C．下临界雷诺数
D．都不是
参考答案：D
The number of people present at the meeting ________ about 1000, a large number of whom ________ experts from abroad.
A．was; was
B．were; were
C．was; were
D．were; was
A．酸和甘油
B．氨基酸
C．葡萄糖
D．肥皂
