As soon as he finished reading the collect letter, than he flew into a rage and tore it into pieces.

The most suitable phrase that should replace the phrase given in bold is “he flew into a rage”. It is to be noted that after ’As soon as, So long as, As long as’ we do not use ’than’. Except for option 4 none other options are in absolute grammatical syntax. Hence, it becomes the most viable answer choice.