Directions: Choose the option that fills up the blanks most correctly.

The inventor had to ________ his idea for several months.

Option (1), 'organize' is not incorrect but doesn't seem perfect fit for this blank, so, just keep it for time being. Option (2), 'sift through' is inappropriate because we sift through pages. Option (3), 'mull over' is much better because we mull over an idea. Option (4), remember is again inappropriate because the term has to be used in relation to a period of time and not a particular incident. So, among all given choices, we can clearly see that option (3) is correct answer.