If students do not understand what is taught in the class, the teacher should

Reteaching the lesson with suitable examples makes the abstract idea concrete and clears the difficulty.

Merely repeating the lesson gives the same words that already failed to communicate.

Checking previous knowledge is useful before teaching but does not by itself explain the present confusion.

Proceeding to the next topic abandons students who have not understood.

Moving from concrete examples to abstract ideas follows the maxim concrete to abstract.

Examples bridge new content to learners' experience and aid meaningful learning.