The vector bold ( a₁ ) is in ( W ) if and only if ( a₁ ) can be written in the form ( c₁ a₁ + c₂ a₂ + c₃ a₃ ) with:

a) ( c₁ = 1, c₂ = 0, c₃ = 0 )
b) ( c₁ = 0, c₂ = 1, c₃ = 0 )
c) ( c₁ = 0, c₂ = 0, c₃ = 1 )
d) ( c₁ = 1, c₂ = 1, c₃ = 1 )