The external load per unit length of

• A. a pipe laid on, or projecting above the undisturbed ground and covered with fills, is proportional to the square of the external diameter of the pipe
• B. a flexible pipe burried in narrow trenches and thoroughly compacted side fills, is proportional to the product of the width of the trench and diameter of the pipe
• C. a rigid pipe burried in a narrow trenches and thoroughly compacted side fills, is proportional to the square of the width of the trench
• D. all the above.