1)Ten Kilometers (A)/ are a long (2)/ distance to walk (C)/ No error (D).
Error in part B
Use ‘is’ instead of ‘are’.
2)Patience as well as (A)/perseverance are necessary (2)/for success (C)/ No error (D).
Error in part B
Use ‘is’ instead of ‘are’.
3)He is one of those (A)/writers who has won acclaim (2)/ the world over (C)/ No error (D).
Error in part B
Use ‘have’ instead of ‘has’.
4)Everyone of the films (A)/ you suggested (2)/ are not worth seeing (C)/ No error (D).
Error in part C
Use ‘is’ instead of ‘are’.
5)The ebb and flow of the tides (A)/are now (2)/ understood (C)/ Nor error (D).
Error in part B
Use ‘is’ instead of ‘are’.
6)Nine Tenths (A)/of the food (2)/have rotted away (C)/ No error (D).
Error in part C
Use ‘has’ instead of ‘have’.
7)Either Sohan or his friends (A)/is to be blamed for (2)/ this mischief (C)/No error (D).
Error in part B
Use ‘are’ instead of ‘is’.
8)Every boy and every girl (A)/ were happy to (2)/ receive a gift (C)/ No error (D).
Error in part B
Use ‘was’ instead of ‘were’.
9)More Student (A)/than one have participated (2)/in the annual function (C)/No error (D).
Error in part A
Use ‘students’ instead of ‘student’.
10)Many a (A)/ man were (2)/ killed (C)/ No error (D).
Error in part B
Use ‘was’ instead of ‘were’.
11)A number of (A)/ student has (2)/ taken the test (C)/ No error (D).
Error in part B
Use ‘students have’ instead of ‘student has’.
12)I am not one (A)/of those who will trust (2)/everyone whom (C)/I meet/ No error (D).
Error in part C
Use 'they' instead of 'I', antecedent of relative Pronoun who is those which is plural therefore sentence should be in plural form.