The correct option is B Delete sentence (5)
Sentence 5 is redundant here- it is unnecessary with respect to the central issue of the paragraph . It ideas mentioned in sentence 4 does not need to be followed by idea of 5. Sentence 6 is more fit to follow 4 and not sentence 5. The deletion of sentence 5 won't make a difference in the structure and context of the paragraph. If we follow through with any of the other steps mentioned in the choices, the passage structure and meaning of the paragraph will be distorted. So, our answer is C.