Which of the following words cannot be used to describe today's lenses

A．the principles of designing lenses
B．techniques of making contact lenses
C．the design of photographic lenses
D．styles of lenses

A．the final goal and the means by which it can be reached are known
B．perfect solutions to a problem can be found
C．any one decision at any point along the way to the goal can bring numerous possible results
D．both A and C