Isn't gerund here a noun phrase?

[CoraT203]

Unlike using spices for cooking, in medicinal usage they are taken in large quantities in order to treat particular maladies.

A Unlike using spices for cooking, in medicinal usage they are taken

B Unlike spices that are used in cooking, in using spices for medicine, they are taken

C Unlike cooking with spices, taking spices for medicinal use is done

D In cooking, small quantities of spices are used, whereas in medicinal usage spices are taken

E In cooking, the usage of spices is in small quantities, whereas in medicinal usage they are taken

My questions are :
1. isn't the cooking.... , taking..... are gerund here. so it is not verb. then why c is wrong？
2. What is D, though it is the correct answer.

[Sage Pearce-Higgins]

Please read the forum guidelines before posting: quote the source of the problem, the correct answer, and search to see if the problem has already been posted.

There's quite a long discussion of this problem here https://www.manhattanprep.com/gmat/forums/unlike-using-spices-for-cooking-in-medicinal-usage-t1062.html.

I agree with you that 'cooking' and 'taking' are both gerunds (and would be parallel), but the problem with answer choice C is the phrase 'taking spices for medicinal use is done in large quantities'. This is illogical: it's the spices, not the 'taking', that is the large quantity. This is just the kind of sentence that sounds okay, but is nonsense if you read it slowly, that GMAT will throw at you.