Ответ:

1 The lily-of-the-valley isn't a beautiful spring flower

2 Masha didn't spent her holiday on the Black Sea coast

3 Doesn't the Mississippi the longest river in the USA flow south

4 The Ural is not a famous chain of mountains in Russia

5 what countries doesn't Russia border on

6 the forest doesn't stretch to the east or to the west from this place

7 Sunday wasn't such a perfect day for our boat trip

8 the Great Plains of the USA aren't situated in the central part of the country

9 There isn't a fantastic valley high in the mountain

10 the water of the rivers flowed slowly and it wasn't to easy to swim in it