Read the text below and decide which answer best fits each gap

Read the text below and decide which answer (A, B, C or D) best fits each gap. E-mail, and chat rooms let children communicate (18) _____ friends and family members. They can also allow children to connect with people that they have never (19) _____ in person. Knowing a little about each of these communication services can help parents (20) _____ children safer while online. Through e-mail, (21) _____ can easily send and receive messages. These messages may also have text, audio, and picture files attached. Signing up for an e-mail account is simple (22) _____ most services offer them for free. Sometimes these messages contain viruses, or other inappropriate content, so parents should warn children to be wary of emails from (23) _____ people.
18. A. to B. with C. for D. through
19. A. met B. gone C. asked D. called 2
0. 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