The correct answer is B) A short splice in a line doubles the size of the line. A short splice is a method of joining the ends of a line by interweaving the strands of the two ends. This process effectively doubles the diameter of the line at the splice, making it stronger and more durable. The short splice is commonly used in applications where the line needs to pass through a block or other fitting, as it does not create a significant change in the line's overall diameter. The other options are incorrect because: A) a short splice is not specifically required for a line passing through a block, C) the short splice increases rather than decreases the size of the line, and D) a short splice can be used in both synthetic and wire rope, not just wire rope.