Réponse :
1) 1- he arrived /had already rung
2- I saw /had never heard
3- She changed / had already sold
4- was / they had expected
5- had read
6- I met /I hadn't seen
ex 2
1 was allowed / had declared
2 arrived/ had already gathered
3 entered/ had refused
4 arrived/ accepted
5 had enrolled/ lost
Explications : pastperfect (pratiquement équivalent du plus que parfait français.)
C'est un temps du passé. On s'intéresse à une 1re action (généralement au prétérit) alors que la deuxième action au pastperfect s'est déroulée avant la première.