1. By last year, twenty schools in this province (be) built.
--> were
2. When i got to the party, they (go) home.
-->went
3. She went to the department after her (clean) the floor .
--> cleaned
4. Before he died , he (be) ill for several days .
--> was
5. Many people (move) to the new place before the storm occurred .
--> moved

1. By last year, twenty schools in this province (be) built.
=>were
2. When i got to the party, they (go) home.
=>had gone
CT:when S V2/ed, S +had V3/ed
3. She went to the department after her (clean) the floor .
=>had cleaned
CT: S+ V2/ed after S + had V3/ed
4. Before he died , he (be) ill for several days .
=>had been
CT:Before S+ V2/ed ,S + had V3/ed
5. Many people (move) to the new place before the storm occurred .
=>had moved
CT: S + had V3/ed Before S+ V2/ed