jì / rán / zhè / shì / shàng / jí / de / chéng / mìng / wǒ / men / jiù / bì / xū / àn / yāo / qiú / zhí / xíng

既然这是上级的成命，我们就必须按要求执行。

Since this is an order already issued by our superiors, we must carry it out as required.