谁能帮忙总结一下ago与 before的区别,最好能全面一点

谁能帮忙总结一下ago与 before的区别,最好能全面一点
用ago ,before 填空
1,I met him three years___________
2,I had met him three years ________________。
3．I remember seeing you somewhere 2 years______.
4．I have read the novel______.
5．She said she had met Tom two days______.
6．She has been there since 3 years_______.
7．How long_____did you get to know her?
8.I called him up last night，but his mother told me he had left for Wuhan two days____
9 She said that she had married him five years _______.
10,He said he had arrived here a day ___________
11,He said he had arrived here the day___________
12,I graduated from the college twenty years ________.
13,I was asked what I was doing a month __________.