1. better than "Best than" is incorrect because two things are being compared.
2. This sentence is correct.
3. flattest and driest "The flatter and drier" is incorrect because there are more than two continents.
4. less severe than not as severe as "As not severe as" is incorrect because one of two things compared does not have as much of the particular qualityi incorrect word order.
5. This sentence is correct.
6. tougher "Tough" is incorrect because it is not in the comparative form.
7 This sentence is correct. 8. the largest sailing ship-The article "the" is used with the superlative.
9. Turkey's largest city The article "the" should not be used with the possessive form. 10. This sentence is correct.