语法：讨论和置疑

Scientists have suggested that once every 10 minllion years or so a truly colossal object from space cut thru the atmosphere and slam into the earth, (sending up a global part of dust that bolts) out of the sun, alters the climate and change the course of the evolution by boiling off many plant and animal species.
B) thus sending up a global pull of dust to bolt
C) thereby sending up a global pull of dust to bolt

这是往年的考题，答案是a但是大家再看看OG的这道题目：
245. Unlike （Schoenberg's twelve-tone system that
dominated ）the music of the postwar period, Bartok founded no school and left behind only a handful of disciples.
(A)Schoenberg's twelve-tone system that dominated
(B)Schoenberg and his twelve-tone system which dominated
(C)Schoenberg, whose twelve-tone system dominated
(D)the twelve-tone system of Schoenberg that has dominated
(E)Schoenberg and the twelve-tone system, dominating
C, the best answer, is the only choice that makes a logical comparison: Unlike Schoenberg, .. . Bartok. In E, the comparison is illogical and the modification is ambiguous. Schoenberg and his system, as a unit, are not only compared to Bartok, an individual, but also credited with having formed a school. The verb phrase dominating ... is called a "squinting modifier" because it looks in both directions: given the structure of the sentence, it could be meant to modify either Schoenberg and the twelve-tone system or Bartok.
答案E的解释就是说分词dominating 是"squinting modifier" ，不知道他是修饰前面还是后面，那么上面的那个题目为什么选a就可以呢？也是一个分词，不能确定是修饰前面还是后面

请大虾讨论