the correct answer is:
since prehistoric times, milk has been a vital source of nutrition for human beings. however, some doctors and nutritionists believe that consuming milk can be detrimental to our health.
the use of the word "however" in the beginning of passage 2, indicates there is a contradiction of the previous sentence. even though milk has been a vital source of nutrition for human beings, some doctors and nutritionist believe it can be detrimental.
while the others went swimming, we made a sa...