A career in the medical profession, which requires an enormous investment of time and money, do not guarantee success as there is so much competition.
(A) which requires an enormous investment of time and money, do not guarantee success as there is so much competition
A career do not guarantee success , does is used for referring the third entity which is singular
I do this , we do this (correct)
career do this (wrong), career does this (correct)
(B) which requires an enormous investment of time and money, does not guarantee success since there is so much competition
does - is the correct form, since is correctly used to explain the reason
(C) requiring an enormous investment of time and money, without guarantee because there is so much competition
A career , requiring lot of investment, without guarantee because ... there is no action or verb in the first part, so sentence appears disconnect
(D) requires an enormous investment of time and money, and it cannot guarantee success because there is so much competition
career requires lot of investment and it cannot guarantee success because... does 'it' point to profession or career.. also this sentence makes it mandatory about career needing lot of investment which is not intended meaning
(E) requires that an enormous investment of time and money be made and success cannot be guaranteed due to the competition
here also it suggests career demands lot of investment to be made. success cannot be guaranteed as a separate element in the list, no more has the connection with career
and use of due to is wrong to specify the reason..
B is the answer!