30 students of a class were tested on Archery. These students were than given a seven day training course in archery. When the students were tested again after the course they showed a forty percent improvement in accuracy. Thus it is clear that the course is helpful in improving the accuracy in archery.
Which of the following if true weakens the argument above?
(A) A three day short term course conducted by the same tutors did not yield proportionate increase in efficiency.
(B) The thirty students also practiced archery daily for two hours apart from fulfilling the requirement of the course.
(C) In an archery competition held just after the course, where the students from other schools participated as well, the students of this referred school couldn't win any prize.
(D) Similar training courses conducted for other sports did not improve the efficiency of the participants.
(E) The same course conducted for some senior students of the same school resulted in an improvement of only thirty percent accuracy in archery.