recommend omitting 'in'

A : “Everyone should do his or her best in whatever situation he or she finds himself or herself in.” I am definitely using this next time I need to reach a word quota on my English paper.

B : A - If you do choose to use it, omit the final "in." It is redundant.

C : B - It may be a redundancy to the minimalist department of the grammar police -- but as grammar police are way too often out of touch with the linguistic needs of the language, the Minimalist Department is quite possibly the worst of all in that regard - taking their cluelessness to extremes that embarrass even other grammar cops. Sometimes some redundancies are necessary for the sake of clarity. The "in" you are complaining about is a prime example.

D : C - Just my two cents worth: the sentence had clarity without the redundancy.

? I'm not sure whether C is right or D is right in that case.