The correct response to this question is (E).
The original version (A) is redundant in its use of "job" twice; the first occurrence is unnecessary. Also, "at times" is idiomatically improper here. (Two proper idioms here would be sometimes and occasionally.)
(E) corrects both problems by omitting "job" from the beginning of the sentence and by replacing "at times" with "sometimes."
Both (B) and (C) fail to correct the redundancy, and they are awkwardly constructed.
In (D), the phrase "In some cases some" is awkward. Moreover, this phrase alters the meaning of the original version by going too far in limiting the situations in which a demonstration is requested.
"Start By Doing What Is Necessary ,Then What Is Possible & Suddenly You Will Realise That You Are Doing The Impossible"