In which sentence is the underlined word an indefinite article?

a.

our dog ate the bone quickly.

b.

one bird flew over us.

c.

i need a pair of socks.

Which is (not) a strategy you would use when revising the overall structure of a comparison and contrast essay a) color-code supporting details in your draft b) focus on eliminating details not related to the them c) circle unrelated or unfocused details in the draft d) combine details that provide facts or statistics