The correct answer is - a. Pangaea.
Pangaea is the super-continent which contained all the continents we know nowadays in it, and they were all one big whole. This continent existed during the late Paleozoic and early Mesozoic eras, approximately from around 335 million years ago until 175 million years ago. Because of the intense geologic activity, around 175 million years ago, Pangaea started to break apart, thus little by little the modern day continents started to take shape.