In the final episode of the Superquark season, the stunning images from the BBC documentary Discovering Africa. The episode continues with the story of an entire region that owes its name to the founding of a Roman city: Aosta. Alberto Angela travels the land at the foot of Europe's peaks, exploring a little-known heritage. Next, a report on viruses: invisible enemies that know how to infiltrate our cells, as the Covid-19 epidemic has taught us. But if we "reprogram" them in the lab, they can become extraordinary allies against genetic diseases, as Barbara Bernardini explains. Marco Visalberghi recounts how, after thirty years of observations, an international team of astrophysicists has published a new, astonishing confirmation of Einstein's theory of relativity. They freshen the air, purify it, stop the rain: trees in the city.