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a. I want to work in the marketing field, in which I'm interested.

b. I want to work in the marketing field that I'm interested in.

c. I want to work in a marketing field that I'm interested in.

In terms of meaning, does a=b? OR

In terms of meaning, does b=c?

My guesses:

a= I want to work in the marketing field. Further, I'm interested in this field.

b= I feel this doesn't work. The definite article doesn't seem to work with the restrictive clause that follows.

c= I only want to work in a certain type of marketing field-- i.e., one I'm interested in.

Thanks
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A does not equal either B or C.
A considers 'marketing' a single field; B and C consider that 'marketing' is composed of several fields.
Both B and C are fine. B suggests (but not not state explicitly) that he is interested in only one of those fields; C suggests that he is interested in several of those fields.
Comments  
Students: We have free audio pronunciation exercises.
Mister MicawberB suggests (but not not state explicitly) that he is interested in only one of those fields; C suggests that he is interested in several of those fields
I believe that was a good question followed by a great answer. Thank you.
What about the meanings for?

a. I want to work in the marketing field, that I'm interested in.

b. I want to work in the marketing field, which I'm interested in.

c. I want to work in a marketing field, which I'm interested in.

a. I don't think this is grammatical.

b. Considers marketing as a single field, and I'm interested in it.

c. I don't think this is correct either.
a. I don't think this is grammatical.-- Me neither.

b. Considers marketing as a single field, and I'm interested in it.-- Yes

c. I don't think this is correct either.-- It leaves 'which' a vague referer, doesn't it? I think there's a style rule against it. I want to work in a marketing field, which I'm interested in doing.
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