The word "pinpoint" (Line 3, Para. 1) basically means______.

A．They invented false theories to explain things they didn't understand.
B．They falsely claimed to know all about nature.
C．They did not believe in results from scientific observation.
D．They paid little attention to the problems they didn't understand.

A．He is depressed because of the ignorance of scientists.
B．He is doubtful because of the enormous difficulties in scientific research.
C．He is confident though he is aware of the enormous difficulties in scientific research.
D．He is delighted because of the illuminating scientific findings.