【正确答案】 C

【答案解析】[理由] 空格内置入that之后，形成that引导的名词从句that they would be delivered within a week(它们会在一个星期之内送达)，此名词从句与之前的名词the understanding(了解)形成同位语，合乎语意及用法，故(C)应为正选。
[例] We finally came to the understanding that he was innocent.
(我们终于了解到他是无辜的。)
由上得知，the understanding之后通常置that引导的名词从句，使该that从句当作the understanding的同位语，形成固定用法。