Please check it carefully.
X is put where there will be no article:
1. X Philosophy is a difficult subject because it is based on X abstract things.
2. and 3. are correct
4. is correct
5. First part is correct. It has a unique attraction. ('an' comes before vowel sounds, not vowels; 'unique' starts with consonant sound)
6. Last week I saw a one-eyed man (rest of the sentence is correct)
7. is correct
8. is correct
9. First part is correct. Friends may become X enemies and the worst enemies friends.
10. France is a European country. the rest is correct.
1. X Philosophy is a difficult subject because it is based on X abstract things.
2. and 3. are correct
4. is correct
5. First part is correct. It has a unique attraction. ('an' comes before vowel sounds, not vowels; 'unique' starts with consonant sound)
6. Last week I saw a one-eyed man (rest of the sentence is correct)
7. is correct
8. is correct
9. First part is correct. Friends may become X enemies and the worst enemies friends.
10. France is a European country. the rest is correct.