The radius of gyration of a rectangular section (depth D, width B) from a centroidal axis parallel to the width is

• A. <img src="/_files/images/civil-engineering/theory-of-structures/86-21-63-1.png">
• B. <img src="/_files/images/civil-engineering/theory-of-structures/86-21-63-2.png">
• C. <img src="/_files/images/civil-engineering/theory-of-structures/86-21-63-3.png">
• D. <img src="/_files/images/civil-engineering/theory-of-structures/86-21-63-4.png">