The correct answer is D. Moderate tone.
A teacher should adopt a moderate tone in his lecture in a class. This means that the teacher should speak clearly and at a moderate volume, and should avoid speaking too quickly or too slowly. The teacher should also avoid using too much slang or jargon, and should make sure that the students can understand what he is saying.
A precise and low tone is not ideal for a lecture, as it can be difficult for students to hear and understand the teacher. An elongated tone can also be difficult to understand, as it can sound like the teacher is dragging out his words. A precise and high tone can be effective in getting the students’ attention, but it can also be tiring to listen to for long periods of time.
A moderate tone is the best option for a lecture, as it is easy to understand and does not become tiring to listen to. It is also the most professional tone to use in a classroom setting.