GMAT Sentence Correction (SC) | Re: Though caterpillars transform large amounts of plant matter

Though caterpillars transform large amounts of plant matter into animal tissue and wastes, and therefore hold an important place in the food chain, they are so voracious that they have become an economic threat to farmers whose crops they eat.

1) The sentence starts with a contrast word 'though'. Look out for contrast in the way sentence is constructed.
2) 'that' here is used as a connector.

3) Though caterpillars.................is a dependent clause and they are so...................is an
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