Success always requires long hours of hard work, even if there is no certainty
that long hard working hours results in success.

A. even if there is no certainty that long hard working hours results
B. although there is no certainty of the long hard working hours resulting
C. even though it is not certain that long hours of hard work results
D. even though there is no certainty that the long hours of hard work result
E. though there is no certainty of long hours of hard work resulting

Source: Experts Global
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Success always requires long hours of hard work, even if there is no certainty that long hard working hours results in success.

A. even if there is no certainty that long hard working hours results ----1. 'hours' is the subject and 'results' is wrong. S-V error 2.' Long hard working hours' is inferior to long hours of hard work

B. although there is no certainty of the long hard working hours resulting --- 'Long hard working hours' is inferior to 'long hours of hard work.'

C. even though it is not certain that long hours of hard work results ---- S-V error as in A.

D. even though there is no certainty that the long hours of hard work result -- looks like the answer

E. though there is no certainty of long hours of hard work resulting --- 'certainty of 'is not as idiomatic as 'certainty that.'

Overall, a subordinate clause at the end of a sentence does not require a comma before it and some puritans may even call such a usage ungrammatical.
Pushpi
Is there any reason for tagging this as a self-made question while it is from Expert Global?

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Success always requires long hours of hard work, even if there is no certainty
that long hard working hours results in success.

A. even if there is no certainty that long hard working hours results
B. although there is no certainty of the long hard working hours resulting
C. even though it is not certain that long hours of hard work results
D. even though there is no certainty that the long hours of hard work result --> correct
E. though there is no certainty of long hours of hard work resulting