There are only four types of true tea.
Why it is true
There are six main types of true tea (Camellia sinensis): white, green, yellow, oolong, black and pu-erh. The difference between them lies in the degree of oxidation and fermentation of the leaves, not in the plant.
Source: National Geographic
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.