The correct answer is Option 4) i.e. within, forAfter reading the sentence we can easily comprehend that Raman is confident that he will be able to speak English under a certain time limit, so we need a Preposition that will convey this meaning. The available options for the first blank are 'for', 'during' and 'within', we can easily negate for and during because 'for' is used to represent a duration of time and 'during' is any time between the start and finish of a set length of time. Hence, we are left with 'within' which is the most appropriate choice as it means under a certain time limit.Now for the second blank 'for' is the most apt option because 'last three weeks' is a duration of time and we use "For" when we measure the duration “ when we say how long something lasts.Complete Sentence: Raman is confident of speaking English within six months as he has been practising regularly for the last three weeks.