ago/before
Ⅰ。 ago adv. “……以前”指从此刻起，若干时间以前，通常与过去连用。如：
① It happened two days ago.这件事发生在两天以前。
② I met him a few minutes ago.我在几分钟以前碰到他。
Ⅱ。 before adv, prep & conj “……以前”指从那时起若干时间以前。通常与完成时、过去时等连用。还可用作前置词或连接词表时间，而ago 则不能这样用。
① He said that he had seen her two days before.他说他两天前见到过她。（表从她说话那时起两天前）
② I had been fine the day before.（那天）前一天的天气很好。
③ I’ve seen that film before.
④ I never met him before.
agree to/ agree with/ agree on（up on）
Ⅰ。 agree to “同意、应允”通常用于同意某件事情（我们可以同意我们自己有不同看法而并不赞同的事情）。如：
① Do you agree to this plan?
② He agreed to my proposal.他同意了我的提议。
③ I agreed to his terms. 我同意了他的条件。
Ⅱ。 agree with “同意、赞同”常常表示同某人意见一致，也可表赞同某件事情。还有“（气候、食物等）适合”之意。如：
① I quite agree with you.我很同意你。
② Do you agree with me ?
③ I agree with all you say.我同意你所说的。
④ His words do not agree with his actions.他言行不一致。
⑤ Too much meat doesn’t agree with her. 吃太多肉对她身体不合适。
[注]：agree with 不能用于被动语态。
Ⅲ。 agree on /upon “对……取得一致意见”指两方或多方就某个问题取得了一致的意见或达成了某种协议。如：
① After discussion the two sides agreed on a cease-fire. 经过讨论，双方就停火问题达成了协议。
② They all agree on the plan.他们对这个计划意见一致。
[注]：此句型可转换成agree in doing sth.如：
① All of them agreed on / upon it. = All of them agreed in doing it. 他们对做这个问题达成了共识。