Verse 31: All of the food ________ sold by the time we arrived at the restaurant.
Past perfect tense: had + PP
The past perfect is used to describe an action that happened before a time in the past or an action that happened before another action in the past.
Identifying signs: by the time + time in the past / by the time + tense QKĐ
=> Answer B (All the food was sold before we got to the restaurant.)
===============