In the second paragraph the author uses an analogy (类比) that assumes that general principles are similar to______.
A) the wood C) the trees
B) technical details D) fixed laws

A．if a person has a background of knowledge, he can read superficially over a wide field
B．an adult can build foundations in science no higher than a young man
C．a thorough grounding in the fundamental sciences is absolutely necessary for a person hoping to derive value from superficial reading over a wide field
D．a mass of detailed technical information is indispensable to creative thinking

A．most scientists are obliged to teach
B．a scientist may cultivate wide interests if he teaches as well
C．in order to keep up with developments in a wider field, teaching and research are both important
D．if a scientist does not teach, he is less likely to absorb diverse knowledge