Correct choice is (c) ‘c2’ is of first preference in shafts
The explanation is: a11, c2, d9, d11, e8 etc. are the first preference for shafts and b9, b11, c8, c11, d8 etc. are the second preferences for shafts. First preference of holes are A11, D11, E11, F7, F8 etc. and B9, B11, C9, C11, D9 etc. are the second preferences for holes.