join the sentences to make one, using relative clauses. decide if they are defining or non defining, adding commas where necessary.
1. several new building have been constructed in Moscow in the last decade. they may be the future wonders of the world.
2. one of them is the mercury city tower. it is the tallest building in europe. it is 339 meters high.
3. the new tower is a mixed office and residential building. it was designeed by mikhail posokhin and frank williams.
4. next door to it is federation tower. it is a complex of two towers built on one podium. it is under construction now. it will reach 506 meters.
5. the mercury tower and the federation tower are high-rise structures. they are actively used as sightseeing objects. they both have won prestigious awards.