(C) is correct.

Issue: Whether the plaintiff can still recover despite the fact that an intervening force caused the injury.

Rule: A  direct  cause  is  where  the  injury  results  directly  from  the  breach  of  duty  and  there  is  no  other event that contributes to the plaintiff’s injury. A superseding cause occurs when an intervening act is both unforeseeable and causes an injury different from the one which would have been caused by the defendant’s breach alone. Note  that  if  the  intervening  event  was  foreseeable, then  it  is  not  superseding.  When  there  is  a  foreseeable  intervening  force  rather  than  a  superseding  cause,  the  original  defendant  is  still  the  legal  cause  of  that  injury  and  is  responsible  to  the  plaintiff  for  all  foreseeable damages, including the harm caused by the intervening force.

Analysis: Here, it is foreseeable that a lawnmower might come in contact with a stick.  Thus, the manufacturer is still liable for any injury caused by the intervening force (the stick).  Moreover, the injury caused by the blade is a foreseeable injury.

(C)  is correct because the stick is a foreseeable intervening force and the injury caused is also foreseeable.

(A) is incorrect because the lawnmower did not directly cause the injury; it was the lawnmower’s contact with the stick that caused the injury.

(B) is incorrect because a superseding cause is unforeseeable and causes an injury that would be different from defendant’s breach alone. Here, the stick is completely foreseeable and the injury caused is no different than what might occur if defendant’s breach alone caused the injury.

(D) is incorrect because the stick was foreseeable.