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单项选择题

The underlined word "it" refers to which of the following

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

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单项选择题The underlined word hampered in Line 1 Para 2 is closest in meaning to _______.

A．recognized
B．determined
C．solved
D．hindered

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 knowledge systematically.