the issue is not with an idiom of denote or extent itself, but rather with the continuation of the sentence "by the rapid motion of the galaxy away from the Earth." the 'by" indicates that some action has been done BY the motion, requiring the passive form for the previous verb.
Do not be quick to look for idioms - in many cases, idioms are inserted into an SC question just to drag you into playing on the wrong field, that of playing things by ear. Often, there's a stronger reason to eliminate all of the wrong answers and leave yourself with a single right answer. Delay decisions about "idiomatic" reasons to eliminate answer choices until you really have to - focus on other, more solid grammar/logic/style/fit into the rest of the sentence reasons to eliminate an answer choice. If, after looking at the answer choices carefully, yo cannot find a reason to eliminate one or the other, guess by "which idiom sounds better".
inactived wrote:I still have a little concern regarding this question. The OG 10th Ed explains as follows:
Choice A is best because it is idiomatic and because its passive verb construction, has been shifted, clearly indicates that the light has been acted upon by the rapid motion.
In B, the active verb has shifted suggests that the light, not the motion, is the agency of action, but such a construction leaves the phrase by the rapid motion of the galaxy away from the Earth without any logical or grammatical function.
In C, the construction the extent that light is ungrammatical; denotes the extent must be completed by to which.
D incorrectly employs an active verb, shifting, and extent of light is imprecise and awkward.
E is faulty because it contains no verb to express the action performed by the rapid motion.
Does anyone know why "denotes the extend" must be completed by "to which"? After searching on Google, I cannot find any idiom in relation to either "denote" or "the extend".
Many thanks.