Choose the odd one out: PRT, SVX, DFH, KMO.

In PRT the letters stand 16, 18, 20, in DFH they stand 4, 6, 8 and in KMO they stand 11, 13, 15, so each group skips one letter twice over, a gap of 2 and then 2. In SVX the letters stand 19, 22, 24, a gap of 3 and then 2, so the first step is one place too wide. The group is off by a single shift, which is exactly what makes it easy to pass over.