Book-crossers 'release' books (60) _____ by passing them on to friends, or else by leaving them in public places for others to pick up, or 'catch', and then read,
Book-crossers 'release' books (60) _____ by passing them on to friends, or else by leaving them in public places for others to pick up, or 'catch', and then read,
A. either
B. but
C. or
D. neither