Note that point B is the back, top corner of the cube and is not represented with any dot. For a point to be collinear with B and I, it would have to lie on the line BI. Let's highlight BI in the diagram for a visual representation.
From the diagram, we can see that the point C is the only other point that lies on the line BI. It is, therefore, the one point that is collinear with B and I.
