Which word is correctly used in blank #3?

there two apartments in this building for sale which going to look at if we can only remember they're located.

a. where
b. were
c. we're

primary succession occurs in essentially lifeless areas regions in which the soil is incapable of sustaining life as a result of such factors as lava flows, newly formed sand dunes, or rocks left from a retreating glacier. secondary succession occurs

d. groundwater flows through the subsoil and deposits minerals.