It is the responsibility of the to ensure the doctor's orders are written in a manner that is clear, readable, and easy to understand.
a. home health aide
b. supervising registered nurse
c. client's healthcare advocate
d. prescribing doctor

Explanation:

A registered nurse is a professional of the science of medicine who was graduated from a nursing program.

The main job of a nurse is to supervise and be responsible of care delivered by other health professional like doctor. So, the nurse follows up all indications given by the doctor, and supervise that all it's ok. In other words, a nurse is like a "secretary", who works according to the doctor (boss) indications.

In this case, the correct answer is "supervising registered nurse" because she or he has the responsibility of constantly supervise that all indications are being follows as such. Also, option B is the most reasonable, because a home health aide, a client or the prescribing doctor don't have this responsibility.