The correct answer is - A. Tokyo.
Japan is one of the most urbanized countries in the world, and it has multiple cities that exceed the number of one million inhabitants, but there is one that sticks out far above all the others, that is the capital of Japan, Tokyo. Tokyo is the primate city in Japan, and it has the attributes required for it, by being at least twice the size of the second biggest city in the country, and more than twice as important as well.
In order for a city to be a primate city, it has to has population at least twice as big as the second biggest city, and it has to be at least twice as important than that city. Tokyo is by far the biggest and most important city in Japan, but not just in, it is a city that also has a big global influence, and that should not come as weird considering that Tokyo is actually the biggest city in the whole world.