2、Fill in a proper word and the first letter is given．

1．Last year he celebrated his n__________ birthday, and this year he is going to welcome his twentieth．

2．It is common knowledge that English is the most w_________ spoken across  the world．

3．U_________, e-mail is the most popular way to communicate on the Internet．

4．I__________ others while they are speaking is considered to be impolite．

5．The P_________ in Egypt are well-known to the world．