Four sentences are given. You need to find if they are grammatically correct or incorrect and mark the answer accordingly. P. Selection of personnel for airports should be done meticulously. Q. No sooner had I given a graceful reply to the letter when I began to realize what was expected of me. R. The real truth is that science is not man's nature, it is mere knowledge and training. S. Environmental issues are currently at the centre of a heated debate. Correct Answer Only Q is incorrect The correct answer is 'Only Q is incorrect' Key Points In statement Q, the usage of 'when' is incorrect instead, use 'than'. Whenever we use the 'No sooner...than' conjunction and No sooner at the beginning of the sentence then use 'the inversion form of the verb' which is used in the sentence. The rest of the sentences are correct. So the correct statement is→ No sooner had I given a graceful reply to the letter than I began to realize what was expected of me. Confusion Points 'Than' is a conjunction and a preposition on the other hand 'then' is an adverb of time. Let's see some examples- ​She walks far more slowly than her mother. (In this sentence, 'than' is a preposition) I spent years on the dole trying to get bands together and I never worried about money then. (In this sentence 'then' is an adverb.)