【单选题】世界旅游组织在1979年9月第三届代表大会上正式确定每年的( _______ )为世界旅游日。
【单选题】In which type of chromatography, the stationary phase held in a narrow tube and the mobile phase is forced through it under pressure?
【单选题】当x=8,m=-80时,表达式x/sqr(abs(x^2+m)的值是( ) 其中:sqr()为求平方根函数,abs()为求绝对值函数。例:sqr(9)=3,abs(-5)=5
【单选题】In HPLC, the principle for choosing the stationary phase is ( ).
A.
The difference in boiling point
B.
The difference in temperature
D.
The chemical stability