The plate labeled with A is the South American plate, the one labeled with B is the African plate, and the one labeled with C is the Australian plate.
Explanation:
The three plates that are marked on this map are the South American, African, and Australian (Indo-Australian) plates. All of these three plates have a core of continental crust which is surrounded by oceanic crust. The three continents on these plates are South America, Africa, and Australia (plus the subcontinent of India). Despite the three continents being separated by oceans between them at present, it was not like that throughout the past.
In the distant past these three continents were merged, being part of Gondwanaland, accompanied by India and Antarctica as well.
Divergent boundaries arose between them though, so they started moving apart and gradually formed new continents.
As it stands, there is no evidence that these plates will merge again in the next few million years, as the South American plate moves west, the African is actually splitting into two plates, and the Australian is moving toward northeast.
They all existed as a single continent called Pangea. Pangea first began to be torn apart when a three-pronged fissure grew between Africa, South America, and North America.
