Today, the US is part of the International Space Station (ISS), a space exploration and research platform that orbits more than 200 miles above the Earth. It is the size of a football field and has a mass of more than 400,000 kg. No rocket can lift that much weight, so the station was put together piece by piece. The first parts of the ISS were launched in 1988. They were the Russian-built Zarya Cargo Block and the American-built Unity Node. In total, 16 countries came together to build the completed ISS: Belgium, Brazil, Canada, Denmark, France, Germany, Italy, Japan, the Netherlands, Norway, Russia, Spain, Sweden, Switzerland, the UK and the US. Astronauts come and go in shifts of about six months. They study low-gravity conditions in space and how these conditions affect biological, chemical and physical processes. For example, without the pull of gravity, astronauts actually grow taller because their vertebrae spread out. By living and performing experiments on board the ISS, astronauts are paving the way for future missions around the solar system. Based on the passage, which of the following is true about the International Space Station?

A
It is not yet completely built.

B
It was too large to be built at once.

C
It was made by people on every continent.

D
Its gravity conditions are similar to those on Earth.