His way of doing things was different than what the previous intstructor did
- was different than what the previous instructor did
- differed from that of the previous instructor
- was different from what the previous instructor did
- was different from that of the previous instructor
- was different than the previous instructor's
Can anybody suggest the correct answer along with reasoning
- was different than the previous instructor's
- was different from that of the previous instructor
- was different from what the previous instructor did
- differed from that of the previous instructor












