When he was in America he made a journey of several miles _______ (by chance, on purpose, in turn) to see Yellowstone National Park.
The given answer is 'on purpose'. Is the answer suitable for the sentence?
Thank you in advance.
I'd leave it blank. He made the journey to see the park. What was the purpose? To see the park. No need for additional words.
To write "He made a journey on purpose to see the park" is not at all natural where I live. I disagree with the answer in the book, though (perhaps a BrE speaker will chime in) perhaps this use of "on purpose" is more common elsewhere.
We DO say "You did that on purpose!" which means "You intended to do that." It's the sort of thing one child might say to another if the first steps on the second one's foot "accidentally" (but actually, intending to).
For this use of "on purpose" to work, it needs more context.
A: "Oh, so you happened to be in the part of the country?"
B: "No, I made the trip on purpose to see the park."
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.