84. The following is a statement of “algorithm for square-root multiplication” in a secondary school textbook, “The product of the positive square roots of two positive numbers is equal to the positive square root of the product of the two positive numbers.” After teaching, Ms. Guo found that most students learned the expressional representation of this statement, a b ab × = , but did not understand the above statement. Please choose the most effective teaching activity from the following to help students understand the statement. (A)Thoroughly re-teach the concept of the algorithm. (B)Give students corresponding numerical expressions of the statement, such as 23 6 × = , and ask students to describe it with words. (C)Ask students to start with a part of the statement and gradually expand it and then judge the relations among all mathematical objects in the statement. (D) Ask students to do more exercises pertinent to the algorithm.