A.inherent inhibitions. This is the correct option .
If a person has inhibitions, these will probably prevent him / her from letting the imagination and fantasy fly. Imagination is a key factor for a writer. Besides, a shy person will not allow himself / herself to observe what other people do and will not be able to imagine why people behave in funny or mysterious ways.
The other options are desirable for a future writer:
-B.strong vocabulary. ( A writer should have a good command of a wide range of words and expressions.)
C.rich imagination ( This may be the source of inspiration).
D.observational powers ( Writers tend to be good observers of other people's behaviour).