(Q. 11 to 15):- In the following questions some parts of the sentence have errors and some are correct. Find out which part of a sentence has an error and blacken the circle (A, B, C). If a sentence is free from errors, blacken the circle corresponding to (D) in the Answer Sheet.
15. Unless you do not study seriously (a) / you will not pass (b) / the intermediate examination (c) / No error (d)