The titanoboa was the largest snake that ever existed.
Why it is true
The titanoboa, which lived about 60 million years ago, could reach 13 metres in length and weigh more than a tonne. Its fossils were found in Colombia and reveal that it lived in warm, humid areas similar to a tropical swamp.
Source: Nature
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.