1. Use of ‘when’ and ‘while’: Proper attention must be paid to these words. ‘when’ indicates a general sense and ‘while’ implies a time during the process of doing a work.
1.‘Scarcely’ and ‘hardly’ are followed by ‘when’ and not by ‘than’. Uses - I had scarcely entered the room than the phone rang. (Incorrect) I had scarcely entered the room when the phone rang. (Correct)
1.when a comparison is made by using a comparative followed by ‘than’, the word ‘other’ must be exclude the thing compared form the class of things with which it is compared.
1. When a singular and a plural noun are joined by ‘or’, ‘nor’, the pronoun must be plural. Uses - Either the engineer or his mechanics failed in his duty. (Incorrect) Either the engineer or his mechanics failed in their duty. (Correct)