Discussion from beatthegmat forum: 70: "The underlined part is a modifier of "AGE", the underlined part is describing the age, and it has nothing to do with the Louis Agassiz proposal. Had must have been used in case 1) "Louis Agassiz" did any 2 things in the past...or some thing which affected his "Proposal of age". 2) The modifier of age stated 2 things happend in past. But here the underlined part is just an add on information added by "which", stating only 1 past event about the age. If the sentence was "...an age in which great ice sheets had existed before they melted due to temperate climates", then you could use the past perfect. "
73: by default, "appear" is in the present tense, since we're talking about the way these things appear to present-day observers.
if there were a context that would place "appear" in the past, then you could use the past tense. for instance: to nineteenth-century observers, they appeared to have been equipped... but, absent such a context, you should go with the present, for simplicity (the default assumption is that this "appears" to be the case to present observers).
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in this case, you've also got parallelism between "appear" and "indicates", two descriptions that both describe observations made in the present. since "indicates" is not underlined, that determines the tense context. so your other observation, which is made at the same time, should be parallel to it. |