Finishing their shopping at the supermarket,a middleaged cou

一、动词 discover 后可能跟两种复杂宾语——
1、宾语从句,如：
* She, by accident, discovered that her friend had married. 她无意中发现她的朋友已经结婚了.
2、复合宾语（宾语 + 宾补）,如：
* She, by accident, discovered her friend married （意思同上）
二、根据 discover 的这种特征,此空也可以有这样的两种答案——
1、把“their new car ___”部分视作宾语从句,空白处就需要用 steal 作谓语动词.显然,“被盗”发生在“发现”之前.主句 a middleaged couple discovered 用的是过去时,宾语从句中的盗窃行为就是发生在过去的过去,因此需要用过去完成时 had been stolen,也就是：
* a middleaged couple discovered (that) their new car (had been stolen).
2、把“their new car ___”部分视作复合宾语,即 their new car 是宾语,空白处是宾语补足语.车是被盗的,要求用 steal 的过去分词 stolen 表示被动.也就是：
* a middleaged couple discovered their new car (stolen).
三、如果是 a middleaged couple discovered their new car (was stolen) ,主句和从句的谓语动词同属过去时,表示“发现”和“被盗”几乎是在同时发生,也就是说,中年夫妇还可以看到盗贼在逃离,这在情理上是说不通的.