● 约定

我保证。
I promise.
You can't tell anyone. (你不能告诉任何人。)
I promise I won't. (知道,我保证。)

我不能保证。
I can't promise. *“不能保证,但可以试试”。表达想帮助对方的心情。
You have to come. (你也来吧!)
I'll try but I can't promise. (我争取去,但不能保证。)

一定。
Will do.
Remember to bring the report. (记住带上你的报告。)
Will do. (一定带来。)

我发誓。
I swear. *语气强烈。
Are you sure? (是真的吗?)
I swear. (我发誓。)

请相信我。
Trust me.
I'm not sure. (我没有把握。)
Trust me. (请相信我。)
Believe me.
I know what I'm doing.
You can trust me.
Trust in me.

说到就得做到。
A promise is a promise!
I'm sorry I can't help you. (对不起,我帮不了你。)
You said you would. A promise is a promise! (你说过你可以,说到就得做到。)
You promised! (你不是答应我了吗!)
You can't go back on your promise now! (你现在不能食言。)