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We use the past perfect (or the "double past") when we have two discrete events in the past; the older of the two events takes the past perfect.
In this particular sentence, we have to be very careful. "led" is a discrete event in the past, so an earlier related event would take the past perfect. However, "existed" isn't related to "led";
it's actually related to the "are now" at the end of the sentence. Since "are now" is the present, we use the simple past "existed" to show the relationship between those two actions.
quote：
more knowledge on past perfect：
note that the past perfect can be used, roughly speaking, in two different circumstances:
1) for past actions that were ongoing until, or relevant to, a later past action (this is what you're thinking about);
OR
2) for past actions that were ongoing until, or relevant to, a later past TIME MARKER.
for #2, the second time marker could be something explicitly mentioned in the sentence.
before the introduction of soft landing mats, high jumpers had been forced to use the western-roll style of jumping
--> note that there is no second verb, but "the introduction of soft landing mats" is a time marker.
however, if the context of the sentence clearly IMPLIES a second time marker, then that second time marker may not even have to be mentioned explicitly. |
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