We ____ the whole safety briefing again last Friday because two new drivers had joined the depot.

Բացատրություն

A finished action anchored by "last Friday" calls for the past simple, and this verb keeps three separate shapes rather than adding -ed. The participle "done" cannot stand alone as a tense — it needs an auxiliary such as have — while the base form "do" would leave the sentence in the present despite the past time marker.