18. A. to B. with C. for D. through
19. A. met B. gone C. asked D. called
20. A. save B. protect C. surround D. keep
21. A. receivers B. messengers C. users D. partners
22. A. due to B. because C. because of D. in order to
23. A. known B. well-known C. unknown D. unpopular
24. A. every B. something C. nothing D. anything
25. A. conversations B. meetings C. letters D. users