The bold word "it" refers to which of the fallowing

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.

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.