Sentence Correction

In feudal Korea, cattle were traditionally used as beasts of burden, rather than as a food source, and fish were the primary source of protein in the typical diet.

cattle were traditionally used as beasts of burden, rather than as a food source, and fish were
cattle were being used as beasts of burden, rather than as a food source, and fish were providing
cattle were traditionally used as beasts of burden, rather than as a food source, with fish being
the traditional use of cattle was as beasts of burden, rather than for the provision of food, and fish were
cattle were traditionally used for beasts of burden, rather than for a food source, and fish were

i think the answer should be E instead of A why is it A?

"Used for a" is completely different from "used as a"
I think thats the key in eleminating E.

Yup used as is the right usage for the above sentence.........because we are giving example in the sentence........used for is not used to give example