对一个文件显示双单词

1，首先有一个文件data
tao@debian6:~$ cat data
hello hello about is
is is are you ok be
yes no NO are are
jerry jerry jerry JERRY
She's my girlfriend

2，创建一个管道线，显示所有的双单词，如hello hello
tao@debian6:~$ cat data | tr -cs [:alpha:]\' "\n" |uniq  -c |grep 2|awk '{print $2}'
hello
are