Answer:
c. office. Her
Explanation:
lets interchange them to see which gives the best feel or makes the sentence the clearest.
a:
Lorna did not last long in Mr.Wolcott's office, because her long fingernails made accurate typing impossible, and her abrasive manner scared away too many potential clients.
this is a bit too long and could be smaller of a phrase
b:
Lorna did not last long in Mr.Wolcott's office her long fingernails made accurate typing impossible, and her abrasive manner scared away too many potential clients.
there is no separation between the two words and again the text is far too long
c:
Lorna did not last long in Mr.Wolcott's office. Her long fingernails made accurate typing impossible, and her abrasive manner scared away too many potential clients.
this makes two separate points but also does not need a 'because' or 'since' due to the sentence following providing that for you.
your answer is c.
hope this helps:)