Which of the following statements regarding the radius of a crank (of a reciprocating steam engine) is true?

• A. Thrice the radius of the crank is equal to the stroke of the piston
• B. One-third the radius of the crank is equal to the stroke of the piston
• C. Twice the radius of the crank is equal to the stroke of the piston
• D. half the radius of the crank is equal to the stroke of the piston