You've probably come (3)_____ an example of 'book-crossing', a book-sharing movement started in 2001 by American software developer Ron Hornbaker,
You've probably come (3)_____ an example of 'book-crossing', a book-sharing movement started in 2001 by American software developer Ron Hornbaker, whose stated aim is to 'make the (4)_____ world a library'.
A. away
B. along
C. across
D. aside