Why in the following sentence, "by now" doesn't work? Is there any grammatical justification? -......we have traveled 500 miles. I know already that "so far", "up to now" and "until now" all work here and mean exactly the same, but I racked my brain and searched a lot. Finally I got to a deadlock and decided to ask it. (Though I had asked it in the following link one day ago, but no one had answered it before posting this question.) ……………we have traveled 500 miles - Fill in the blank