In the following questions, a part of the sentence (a word or a phrase) has been highlighted in bold. Four different ways of writing the word or phrase has been given in the options (2), (3), (4) and (5). Find the correct replacement of the given bold word or phrase. If the given word or phrase is grammatically correct, then select option (1). Option (1) repeats the same word or phrase.

Understanding the whole lesson at one go was a fairly difficulty job for him but somehow he managed to do that.