The correct answer is B) is used in running rigging. A long splice is a type of rope splice that is commonly used to join two ropes or to create a loop in the end of a rope. It is a strong and secure connection that does not significantly increase the diameter of the rope, making it well-suited for use in running rigging (lines that move during operation, such as halyards, sheets, and braces). Unlike the other options provided, a long splice is not limited to use on fiber rope, does not weaken the line, and does not double the size of the line.