He wrote a very formal letter of apology to Douglas.

他写了一封非常正式的道歉信给道格拉斯。

We received a letter of apology.

我们收到了一封道歉信。

She wrote a letter of apology but only under protest.

她无奈之下写了一封致歉信。

I mailed a letter of apology.

我发了一封道歉信。

She sent him a letter of apology.

她给他寄了一封道歉信。