Ex.1.

2. The Nile - it's a river, while other two are the mountain ranges.

3. China - it's a state, other two are the continents.

4. The Sahara - it's a desert, others are the oceans.

5. Niagara falls - it's a waterfall, others are the sea.

Ex.2

1 - b

2 - e

3 - f

4 - c

5 - a

6 - d