Final answer:
Ignoring the subject or crowd is not a desirable response for maintaining control, as it results in detachment and potential disorder. The other options are proactive strategies that support control and engagement.
Step-by-step explanation:
Among the options listed, encouraging independent thinking is not a desirable response as it may lead to less control of the subject or crowd. While independent thinking is important for a well-rounded education, it may also make it challenging for the teacher to manage the class and maintain control over the subject matter. The other options - ignoring the subject or crowd, promoting open discussion, and providing clear guidelines and expectations - are more conducive to maintaining control and fostering a productive learning environment.