Under the Inland Navigation Rules, a barge at anchor or made fast to a mooring buoy may, in lieu of the standard Rule 30 provisions, carry all-round white lights arranged to mark corner extremities. What minimum visibility range must those lights meet?

Why C is correct

33 CFR §83.30(j) specifies that a barge or group of barges at anchor or made fast to mooring buoys that uses the alternative corner-extremity lighting arrangement must carry unobstructed all-round white lights of an intensity visible for at least 1 nautical mile. The same 1-nautical-mile requirement applies to the lights described in §83.30(i) for barges required to display lights under §83.30(h).