请问潮差是（）。
A．相邻高、低潮的潮高之差
B．主、附港潮高之差
C．大潮与小潮之差
D．回归潮与分点潮之差
参考答案：A
The number of people invited ____ fifty, but a number of them ___ absent for different reason.
A．were; was
B．was; was
C．were; were
D．was; were
每题的备选项中，只有1个最符合题意。
采用红外分光分析法对游离二氧化硅进行分析时，其吸收光谱的波长中不包括( )。
A．12.5
B．12.8
C．14.4
D．15.9
