Explanation:

- Option:1, Astronaut: An astronaut is a person trained to travel and work in space. They conduct experiments and explore outer space, which does not involve entertaining people or doing difficult feats for an audience.

- Option:2, Performer comedian: A comedian is someone who entertains people by making them laugh. While they perform, they do not perform difficult physical feats.

- Option:3, Acrobat: An acrobat is an entertainer who performs gymnastic feats, which are often difficult and require physical skill and agility. This matches exactly the description of someone who entertains by doing difficult feats.

- Option:4, Cosmonaut: A cosmonaut is similar to an astronaut but is a term used specifically in Russia. Like astronauts, they work in space, which does not include performing difficult feats as entertainment.