Plastic bags are useful for holding many kinds of food,
by means of
their cleanness, toughness and low cost.
【正确答案】
A
【答案解析】解析：by virtue of意为“凭借……的力量，由于(因为)”；in addition to意为“除……之外”；for the sake of意为“为了”；as opposed to意为“完全不同，截然相反”。根据题意，应选“由于，因为”的近义词。故选A。