Answer:
b. A math teacher explains how he uses PowerPoint in his class.
Step-by-step explanation:
In the given passage of the conversation between MFT and Dave I. Ding, the point seems to be the use of PowerPoint presentation to teach in class. Mr. Ding used this presentation to create drill cards which he uses on his students and also helped in giving him "some extra time for marking and lesson planning" while the students are occupied by the presentation.
But the main point of the whole passage is the interview of math teacher Mr. Ding by MFT for his use of PowerPoint presentation in his class. So, the best summary for the interview is that a math teacher explains his use of PowerPoint presentation in his class.
Thus, the correct answer is option b.