Reading each sentence to find out whether there is any grammatical error in it. The error, if any, will be in one part of the sentence. The letter of that part is the answer. If there is no error, the answer is (d) (Ignore the errors of punctuation, if any).
`("He denied that he had not stolen my purse")/a` `("though I was quite sure")/b` `("that he had.")/c` `("No error")/d`

Explanation

(a) Remove .not.