In which sentence is the underlined word an indefinite article?
a. our mail carrier left one package.
b. the sky is clear today.
c. i found a bag of marbles.

C. I found a bag of marbles.

This is the only sentence that contains an indefinite article. Indefinite articles are "a" and "an" for singular nouns. "some" is the indefinite article used for plural or uncountable nouns.

"the" is a definite article. 

There are only two indefinite articles known in English: "a" and "an". Therefore, the correct answer is c. I found a bag of marbles.

"The", however, is a definite article.

Hope this helps~

By how to move the wires