Past Perfect
The Great Smog of 1952 _____ (make) about 100,000 people sick before it _____ (end).
had made - ended
After the smog _____ (end), the government _____ (pass) a law to clean up the air.
had ended - passed
Approximately 200,000 antelope _____ (die) because the weather _____ (become) hotter.
died - had become