2.

A: Kazakhstan is very cold.

B: Yes, but Greenland is much colder than Kazakhstan.

A: Antarctica is the coldest of all.

3.

A: Cars are very fast.

B: Yes, but trains are faster than cars.

A: Planes are the fastest of all.

4.

A: The Yangtze River is very long.

B: Yes, but The River Amazon is longer than The Yangtze River.

A: The River Nile is the longest of all.