GMAT Verbal Section | Ultimate GMAT Grammar Book: Practice Test 3: Q5 & Q46

Friends,

I need some clarification on the below questions.

Q5. Catherine travels a great deal with her mother andthis is the reason she isn’t available to lead the city Finance Committee.
a) this is the reason she isn’t available to lead
b) this is why she isn’t available in leading
c) this is the reason that Catherine isn’t available to lead
d) this is the reason Catherine isn’t available to lead
e) might this be the reason that she can’t lead

Of course a), b) and e) gets eliminated,
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