In the United Kingdom, police officers are not allowed to join _________ or to go on strike.

单项选择题The direct reason for specialization is ______.

单项选择题The author writes the development of geology to demonstrate ______.

单项选择题We can infer from the passage that ______.

单项选择题The growth of specialization in the 19th century might be more clearly seen in sciences such as ______.

单项选择题From the last paragraph the conclusion can be drawn that ambition should be maintained ______.