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By the time the Chinese (experiment) with kites 2,500 years ago, animal flight (exist) for millions of years.
By the time the Chinese experimented with kites 2,500 years ago, animal flight had existed for millions of years.
Long before the Chinese (start) flying kites, early humans (try) to imitate birds.
Long before the Chinese started flying kites, early humans had tried to imitate birds.
The Chinese (use) kites for measuring and signalling before people (try) to use them for transportation.
The Chinese had used kites for measuring and signalling before people tried to use them for transportation.
Although originally the Chinese (design) kites for military uses, they later (use) them for fun and entertainment.
Although originally the Chinese had designed kites for military uses, they later used them for fun and entertainment.
Before paper (make) kites cheaper, the Chinese royal family (fly) silk kites.
Before paper made kites cheaper, the Chinese royal family had flown silk kites.
Before Steven (start) wearing a hat, we (see) his new haircut.
Before Steven started wearing a hat, we had seen his new haircut.
Before Ronaldo (use) girls' toilet, he (consider) going to the boys' toilet.
Before Ronaldo used girls' toilet, he had considered going to the boys' toilet.
Before the first pterosaur (take) flight, insects (fly) for over 100 million years!
Before the first pterosaur took flight, insects had been flying for over 100 million years!
Before da Vinci (make) a drawing of a parachute, he (study) flight for years.
Before da Vinci made a drawing of a parachute, he had been studying flight for years.
Before the Wright brothers (test) the Flyer for the first time, they (experiment) with gliders and wind tunnels.
Before the Wright brothers tested the Flyer for the first time, they had been experimenting with gliders and wind tunnels.
By the time the storm (hit) the airport, our plane (fly) safely for several minutes.
By the time the storm hit the airport, our plane had been flying safely for several minutes.
My uncle (take) flying lessons for several years before he finally (take) me for a ride in his plane.
My uncle had been taking flying lessons for several years before he finally took me for a ride in his plane.
Bats probably (glide) for hundreds of years before they (evolve) the capability of flight.
Bats probably had been gliding for hundreds of years before they evolved the capability of flight.
By the time Archaeopteryx (develop) some features of modern birds, it (evolve) from dinosaurs for millions of years.
By the time Archaeopteryx developed some features of modern birds, it had been evolving from dinosaurs for millions of years.
By the time the Chinese (invent) kites, people (dream) of human flight for many years.
By the time the Chinese invented kites, people had been dreaming of human flight for many years.
By the time Ryan Carney (be inspired) to study the evolution of flight, scientists (study) dinosaur fossils for hundreds of years.
By the time Ryan Carney was inspired to study the evolution of flight, scientists had been studying dinosaur fossils for hundreds of years.
