The threats to the health of astronauts in space are very different from on earth.
A. ones
B. that
C. it
D. those
网友回答
A. ones
B. that
C. it
(答案→)D. those
解析：考察代词用法。One指代可数名词单数，表泛指；that指代可数名词单数或者不可数名词，后面有定语修饰，表特指。It指代上文出现的同一事物。Those指代可数名词复数，后面有定语修饰，表示特指。本题的those=the threats，后面有on earth修饰。结合句意可知D正确。句意：在太空中对宇航员健康的威胁不同于地球上的威胁。