
Passage: The concepts of physics are usually very standardized and rigorous, and the physical quantities represented by the terms of physics have a clear definition, the method of measurement and the relationship of conversion. Physicists and cosmologists still know nothing about dark energy. "Dark energy" refers to only one of the most profound problems in current cosmology.
Question: Which of the following options is most suitable to follow the above as its conclusion?
A. A."Dark energy" is obviously not a clear physical concept.
B. B.Scientists have no choice but to name a cosmic puzzle with "dark energy".
C. C."Dark energy" refers to the puzzling phenomenon that the expansion of the universe is accelerating.
D. D.Scientists still know nothing about the profound meaning behind the term "dark energy".
Answer: