21. The sun sends out huge amounts of energy, not only to Earth, but to all other planets in the solar system and directly into space. The source of all that energy is nuclear fusion (核聚变) occurring at the sun’s core. The Large Helical Device being developed at the Ministry of Educational Institute for Fusion Science (NIFS) is essentially an “artificial sun” that aims to reproduce this nuclear fusion on Earth.
    “Nuclear fusion is a reaction in which nuclei of light atoms such as hydrogen combine to form nuclei of heavier atoms such as helium (氦). If we can utilize the huge amounts of energy released by this reaction, nuclear fusion will then constitute a completely new, clean and never ending source of energy,” says NIFS Director Atsui Iiyoshl. In many respects, fusion is far superior to the various conventional energy sources currently in use.
     Fusion seems to have tremendous potential as a new source of energy. But to produce fusion reactions on Earth, it is necessary to meet a set of critical plasmatic (等离子区) conditions, including ultra-high temperatures of 100 million degrees or so centigrade - a state that refuses to imagine. To meet this challenge, Japanese scientists have come up with their own unique helical device that is particularly safe and is suitable for continuous operation.
     The large Helical Device now being developed is expected to be completed by the end of next year, with experiments scheduled to start at the beginning of 1998.(10分)

21.1  The phrase “artificial sun” in the first paragraph probably means “________”.(2分)
A. a man-made sun
B. NIFS
C. the sun’s energy
D. fusion science