IMO B.....
a.Career switchers often schedule interviews with high level managers , believing that the insight of professionals will help narrow down the many choices of career available to graduating MBAs.
Incorrect: The modifier "believing.." mistakenly modifies high level managers.
b.Career switchers , believing that the insight of professionals will help narrow down the many choices of career available to graduating MBAs,often schedule interviews with high level managers.
Correct: Here, the modifier is set apart from the main sentence. The modifier beginning with believing..clearly modifies the Career switchers.
c.Career switchers believing that scheduling interviews with the insight of high-level professional managers will help narrow down the many choices of careers available to graduating MBAs..
Incorrect: It is generally advisable to set off the additional information by modifiers. Another reasoning that may follow is one cannot schedule the interviews with the "Insight". It appears that scheduling is dont with insights instead of high level professionals.!!!
d.Career switchers,believing that interviews with high-level managers whose insight will help narrow down the many choices of careers available to graduating MBAs,often schedule them.
Incorrect: Them is Possesive Personal Pronoun and here it incorrectly refers to graduating MBAs.
e.Career switchers often schedule interviews to narrow down the many choices of careers available to graduating MBAs, believing that the insight of professionals with high level managers will help them.
Incorrect: Here the meaning of sentence is tempered with.The help is spefically directed towards narrowing the choices. Here that emphasis is lost.
I hope the reasoning is lucid. Eagerly waiting for the OA.