Could cities that float   on the sea solve the problems caused by floods and provide food for the world? Some scientists think so. The idea is already being tested and they believe that floating citied will provide more homes for a growing population, without having to use land needed to grow food. And they believe floating areas will allow more food to be grown, so that no one in the world is hungry. In some places, cities that float on the sea are already being planned, A company in the Netherlands called DeltaSync thinks that sea cities will save the world, with more than one in ten people living in them. They say sea cities solve many of the problems the world faces in the 21st century, like not having enough land , more and more people needing homes, fossil fuels   running low and the increasingly serious problems caused by floods. DeltaSync says building in the desert   is not possible because there is no enough water and that developing ways for people to live in space is still too expensive. So they believe the answer is our oceans, which cover over two thirds of the Earth's surface. Their plans for floating areas include using algae   to produce fuel and food. More than a quarter of the land in the Netherlands already lies underwater and scientists there have spent years trying to find ways to deal with it. In the city of Rotterdam they already have floating homes. Bart Roeffen from DeltaSync says: "We have plans for neighbourhoods including roads and, in the end, I believe we can build floating cities on the sea." DeltaSync is a company that wants to build cities   _  .
on land in space on the sea in the desert
Question: Could cities that float   on the sea solve the problems caused by floods and provide food for the world? Some scientists think so. The idea is already being tested and they believe that floating citied will provide more homes for a growing population, without having to use land needed to grow food. And they believe floating areas will allow more food to be grown, so that no one in the world is hungry. In some places, cities that float on the sea are already being planned, A company in the Netherlands called DeltaSync thinks that sea cities will save the world, with more than one in ten people living in them. They say sea cities solve many of the problems the world faces in the 21st century, like not having enough land , more and more people needing homes, fossil fuels   running low and the increasingly serious problems caused by floods. DeltaSync says building in the desert   is not possible because there is no enough water and that developing ways for people to live in space is still too expensive. So they believe the answer is our oceans, which cover over two thirds of the Earth's surface. Their plans for floating areas include using algae   to produce fuel and food. More than a quarter of the land in the Netherlands already lies underwater and scientists there have spent years trying to find ways to deal with it. In the city of Rotterdam they already have floating homes. Bart Roeffen from DeltaSync says: "We have plans for neighbourhoods including roads and, in the end, I believe we can build floating cities on the sea." DeltaSync is a company that wants to build cities   _  .
A. on land
B. in space
C. on the sea
D. in the desert
Answer: