sentence: But this mode of transport is n't so comfortable , especially when we must travel onshore ; then it 's complicated because travelling by boat is allowed only on the sea or any sizeable river , the courses of which are usually placed less conveniently than roads or even railway tracks .
modified: But this mode of transport is n't so comfortable , esspecialy when we must travel onshore , then it 's complicated because travelling by boat is allowed only by the sea or any sizeable river , which courses are usually placed less conveniently than roads or even railway tracks .
transformation: SPELL, PUNCT, PREP, OTHER