This word means the same as the given italicized word. Hence option B is correct.
Option A: 'Front' means 'the most forward part of something'.
Option C: 'Upper' means 'situated above another part'.
Option D: 'Different' means 'unlike in nature, form or quality'.
These words do not mean the same as the given word 'rear'.
So, options A, C and D are wrong.