单项选择题

What is the passage mainly about

A．The scientific revolution in the seventeenth century.
B．Reasons that chemistry developed slowly as a science.
C．The practical aspects of chemistry.
D．Difficulties of organizing chemical knowledge systematically.

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单项选择题

According to the passage, how did knowledge about chemical processes increase before the seventeenth century

A．Philosophers devised theories about chemical properties.
B．A special symbolic language was developed.
C．Experience led workers to revise their techniques.
D．Experts shared their discoveries with the public.

单项选择题

The bold word it refers to which of the following

A．Problem.
B．Material.
C．Difficulty,
D．System.