I'd further this by suggesting that the only thing we could really tell about that angle is a speculative case where the distance AC is actually a diameter. In that case, we can tell that the angle at B (touching the edge of the circle) is actually a right angle. However, even in this case, the angles at A and C could be anything less than 90 (as long as A and C add up to 90).

Given that we don't know that AC is a diameter, we don't even have that much information.

There really is basically nothing to be done here; Answer E.