The correct answer is - A. larger and more rounded.
The modern humans have brain that significantly differs in size, but also in shape, compared to the brains of the hominid ancestors. The brain of the modern humans is larger, by far, and also it is more rounded and better developed, which has also led to the bone structure of the head to be more rounded. The brains of the hominid ancestors were smaller, but also more flattened, which can also be easily seen by the structure of the skull, more elongated and flattened.
It has differences between one ancestor and another, because as the evolution was going, every next ancestor in the line had slightly larger and slightly more rounded brain, so the difference is bigger with the older ancestors, and smaller with the more recent ones.