请教一道语法

Responding to the public’s fascination with-and sometimes

undue alarm over-possible threats from asteroids, a scale

developed by astronomers rates the likelihood that a particular

asteroid or comet may collide with Earth.

A.     a scale developed by astronomers rates the likelihood

that a particular asteroid or comet may

B.     a scale that astronomers have developed rates how

likely it is for a particular asteroid or comet to

C.     astronomers have developed a scale to rate how likely

a particular asteroid or comet will be to

D.     astronomers have developed a scale for rating the

likelihood that a particular asteroid or comet will

E.      astronomers have developed a scale that rates the

likelihood of a particular asteroid or comet that may.

答案是Ｃ　　请问Ｃ的be to放这里理由何在　　我觉得应该直接will　collide with Earth啊　　　谢谢大家指点

C.这样理解：

astronomers have developed a scale to rate how likely a particular asteroid or comet will be （if a particular asteroid or comet is) to collide with Earth

A have developed a scale to rate how likely sth. to clide with Earth will be

谢谢　　那斑斑的意思是这里是一种什么结构啊？到装？为什么把will be放在前边了？？谢谢指点