由于這是個(gè)孤立的句子，沒(méi)有一定的上下文，我們認(rèn)為B和C都可以，只是含義有所不同，用the one為特指，在本句中相當(dāng)于the job；用one為泛指，在本句中相當(dāng)于a job。即：

The best job is the one (=the job) which uses your skill in doing something together with your interest in the subject.

The best job is one (=a job) which uses your skill in doing something together with your interest in the subject.