GMATGuruNY wrote: Even when a non-essential modifier refers to a specific noun within a clause, the modifier must also provide context for the ENTIRE clause.
Consider the following:
Last year John visited New York, where trash is collected every Tuesday.
Here, the non-essential where-modifier correctly refers to New York.
But -- unless John has a special interest in the trash-collecting methods of major cities -- the where-modifier doesn't seem to provide any context for the preceding clause (john visited New York).
As a result, the sentence seems illogical -- even though the referent for the where-modifier is crystal clear.

The same is true for the non-essential COMMA + as seen modifier in the SC above.
While the implied subject in this clause is the rate, the entire modifier must serve to provide context for the preceding clause.
Otherwise, the sentence would be illogical.

GMATGuruNY wrote:
In my post above, I've explained more fully how a COMMA + as seen modifier should function on the GMAT.

C: On Earth, the rate at which trees grow is believed to be among the surest indications of sunspot cycles, as seen in the rings visible in the cross sections of their trunks.
Error 1:
Here, the omitted subject for the COMMA + as seen modifier seems to be sunspot cycles, implying that SUNSPOT CYCLES are SEEN in the rings of tree trunks.
Not the intended meaning.

Mo2men wrote:I have reviewed your old posts and I discovered it is somehow confusing.In those posts, it seems you are convenience that 'rate' provides nonsensical (illogical) meaning in thsi context. Also, you see that 'sunspot cycles' is the implied in 'COMMA + as seen' while ''sunspot cycles' is not the subject of the choices A & C.
I find that your posts contradicts your answer to me in the previous post, in which you mentioned that 'rate' is the subject.Therefore, I believe Error 1 for choice C is not justified.

What so I miss?

Thanks