Answer: C. use active voice in sentences whenever possible
Step-by-step explanation:
Since Maria is writing advertising copy for a client, the good practice for her to follow is to use active voice in sentences whenever possible. Active voice is important as it'll create vivid images and will also make the sentences to be clear, and convincing.
Writing the copy from her own perspective, the use of long sentences, strong words and ambiguous sentences are incorrect. Therefore, the correct option is C.