Topics tested in this sentence are idioms 'Not X but Y' was tested, and maintain parallelism.
We need to find an option which will presents the intent of the sentence, and that is to concentrate not on ‘X’ (one’s present deprivation) but on ‘Y’ (the sense of well-being ones expect). Hence the answer is D, IMO. Let’s find out the errors in other options.
A.
not to concentrate on one's present deprivation
but rather the sense of well-being you. This sentence violate the intended meaning. Dieting is not to concentrate on something, whereas dieting to concentrate on X. Parallelism is not maintained.
B.
not to concentrate on one's present deprivation
but rather the well-being you. Same as option A.
C. to concentrate
not on one's present deprivation
and not the sense of well-being you. The idioms should be not on X but on Y. Parallelism is not maintained.
D. Both parallelism and idioms are maintained here.
This one is correct.E. Changed the meaning of the sentence like option A & B did.