In the second paragraph the author uses an analogy (类比) that assumes that general principles are similar to______.

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

A．superficial reading is valueless
B．a successful scientist usually confines his reading to the problem under investigation
C．a research worker cannot benefit from superficial and "skim" reading over a wide field if he doesn't have a background of knowledge
D．if a research worker has wide interests, he is sure to succeed in his own specialty