If the length of the longest chord of a certain circle is 18, what is the radius of that certain circle?	Choose the most appropriate option.
A) 2.5  B) 9  C) 10  D) 15  E) 20

Rationale: "longest chord of a circle is the diameter of the circle diameter = 2 * radius if diameter of the circle is given as 18 = 2 * 9 so radius of the circle = 9 correct answer - b"
Answer: B