Human populations _____ (decrease), so wild boars _____ (become) a problem.
had decreased - became
By the late 1980s, the perch population _____ (grow) enormously.
had grown
He _____ (not clean) the car because he _____ (think) it would rain, but it _____ (not rain) in the end.
hadn't cleaned - thought - didn't rain
The Nile Perch _____ (be) a river fish before it _____ (be) brought to Lake Victoria.
had been - was
We _____ (not study) the past participle verbs before we _____ (take) the exam, so he terribly _____ (fail).
hadn't studied - took - failed
The lake _____ (not have) such a large predator before the perch _____ (arrive).
hadn't had - arrived
The Great Smog of 1952 _____ (make) about 100,000 people sick before it _____ (end).
had made - ended
James _____ (call) his mother after he ____ (finish) playing soccer.
called - had finished
Before the sun _____ (go down), Rita _____ (find) a good place to watch the fireworks.
went down - had found
After the smog _____ (end), the government _____ (pass) a law to clean up the air.
had ended - passed
I _____ (not go) home in the morning because I _____ (lose) my keys.
didn't go - had lost
Approximately 200,000 antelope _____ (die) because the weather _____ (become) hotter.
died - had become