X, a mill owner, employed independent contractors to construct a reservoir for his mill. During the course of construction the contractors came upon some old shafts and passages on the land of X. The contractors did not block them. When the reservior was filed, water burst through the old shafts and flooded the mines of 'Y'. 'Y' sued 'X'. 'X' was held liable. He could have not been liable if he could show that

A. He was not negligent

B. The liability lay with the contractor who were known to be competent contractors

C. Escape was owing to palintiff's default

D. All the above

Answer: Option C