Answer:
A. Fragment
Step-by-step explanation:
A sentence fragment is an incomplete sentence. Some fragments are incomplete because they lack either a subject or a verb, or both.
This particular sentence lacks a verb. "the marionettes" is the subject of the independent clause. "Operated by wires above the stage" is a participial phrase modifying the subject, i.e. providing some description about the subject; "whose features seemed lifelike" is a dependent clause describing the subject.
As we see, there is no verb to clarify the subject. What does the writer want to say about "the marionettes"? What did they do? or What were they? We have a written fragment, a major writing error.