OG15第99题

paulsmith123

The stars, some of them at tremendous speeds, are in motion just as the planets are, yet being so far away from Earth that their apparent positions in the sky do not change enough for their movement to be observed during a single human lifetime.
(A) The stars, some of them at tremendous speeds, are in motion just as the planets are, yet being
(B) Like the planets, the stars are in motion, some of them at tremendous speeds, but they are
(C) Although like the planets the stars are in motion, some of them at tremendous speeds, yet
(D) As the planets, the stars are in motion, some of them at tremendous speeds, but they are
(E) The stars are in motion like the planets, some of which at tremendous speeds are in motion but

我看了一些帖子和OG，说some of them at tremendous speeds 放在motion后面最好。
“The modifying phrase, some of them at tremendous speeds, is best placed after motion. ”

请问这里正确选项B中的some of them at tremendous speeds在这里是什么结构？ 是同位语吗？ 如果是的话，同位语不是应该修饰最近的名词吗，修饰in motion想不通呀。