Errors in treatment can include a. unintentionally omitting a required signature on the medical record. b. failure to treat in a timely manner. c. illegible treatment notes in the patient's chart. d. prescribing medication correctly.

I believe B should be your only answer. On the healthcare level, you are in error only a certain amount. Omitting a signature on a medical record is against the law (considering you NEED, consent and or orders to be able to do something). Prescribing medications correctly, is actually doing something right. And if you have seen some doctors handwriting, their handwriting is far from legible, that doesn't mean that treatment was inadequate. 

Failure to treat in a timely manner is an error on your part. and should be the correct answer.