A concave pentagon must have at least one internal angle greater than 180 degrees; other provided options regarding angles and side lengths do not have to be true.
The question is about the properties of a concave pentagon. For a pentagon to be concave, it means that at least one of its internal angles is greater than 180 degrees. This is because a concave shape has at least one vertex pointing inwards towards the center of the shape.
Regarding the options provided, option b (at least one of its angles must be greater than 180 degrees) must be true for a concave pentagon. The other options are not necessarily true, as a concave pentagon can have sides of the same length or different lengths and does not have to have all angles of the same measure.