Question

Shortly after we _______，a waiter came over to our table with a smile. A.seated

Shortly after we _______，a waiter came over to our table with a smile.
A.seated　 B.were seated　
C.sat ourselves　 D.had seated
答案选B，为什么不选D

Answer 1

sit和seat均可用作动词。区别如下：
sit为不及物动词，“坐”，如sit down；seat为及物动词，“使……坐下”，如seat sb.或seat oneself或be seated 。
Sit down, please. = Be seated, please.
以下几个都可作为答案：
1. were seated 2. (had) seated ourselves 3. (had) sat down

Answer 2

before或after 引导的时间状语从句，用一般过去时表示过去完成时