Contrast the following pairs of questions:
A. "Does anybody have any questions?"
B. "Let's think of some other examples now of situations in which this principle is applicable."
A. "Does everybody see how I got this answer?"
B. "Why did I substitute the value of x in this equation?"
A. "Who wants me to go over this explanation again?"
B. "What conclusions can we generalize from this specific graph?"
You need to ask yourself, "What do students need to say or do for me to determine the extent of their understanding?" You can then formulate and pose one or several specific questions, which will give a more comprehensive sounding of the class's problems, and questions.