Things are known （）when they unite with the oxygen of the air.
A、
to have burnt
B、
to have been burnt
C、
to burn
D、
burning
【正确答案】：C
【题目解析】：
众所周知，当它们与空气中的氧气结合时会燃烧。be known to do sth. 为…所熟知，固定搭配。
Things are known （）when they unite with the oxygen of the air.
Things are known （）when they unite with the oxygen of the air.
to have burnt
to have been burnt
to burn
burning
众所周知，当它们与空气中的氧气结合时会燃烧。be known to do sth. 为…所熟知，固定搭配。