one LR question.

a  survey  was recently conducted among ferry passengers on the north sea. among the results was thsi: more of those who had taken anti-seasickness medication before their trip reported symptoms of seasickness than those who had not taken such medication. it is clear, then that despite claims  by drug companies that clinical tests show the contrary ,people would be better off not takin ganti-seasickness medications.

which one of the following, if true, would most weaken the conclusion above?

a given rough enough weather, most ferry passengers will have some symptoms of seasickness.

b the clinical tests reported by drug companies were conducted by the drug companies' staffs.

c people who dont take anti-seasickness medicaton are just as likely to respond to a survey  on seasickness as people who do

d the seasickness symptoms of the people who took anti-seasickness medication would have been more severe had they not taken the medicaiton

e people who have spent money on anti-seasickness medication are less likely to admit symptoms of seasickness than those who have not

which one should be chosen?