Before Amelia Earhart crossed the Atlantic, she _____________ for years to become an experienced pilot. (train), had been training, Before Charles Yeager broke the sound barrier, he _____________ military aircraft for many years. (fly), had been flying, Before the first commercial airplane took off, engineers _____________ ways to make aircraft safer. (develop), had been developing, Before Louis Blériot crossed the English Channel, pilots _____________ to improve the reliability of airplanes. (work), had been working, Before Santos-Dumont achieved powered flight, he _____________ balloons and airships for several years. (design), had been designing, Before the jet engine became widely used, engineers _____________ on alternative propulsion systems. (work), had been working, Before the first passenger aircraft entered service, airlines _____________ new routes across Europe. (plan), had been planning, Before the historic flight, the Wright brothers _____________ their aircraft under strong winds. (not / test), had not been testing, hadn't been testing, Before Amelia Earhart disappeared, she _____________ long-distance flights for several years. (attempt), had been attempting, Before helicopters became common, inventors _____________ different ways to achieve vertical flight. (investigate), had been investigating, Before the first successful jet aircraft took off, scientists _____________ the behavior of air at high speeds. (study), had been studying, Before commercial aviation expanded, most people _____________ by airplane regularly. (not / travel), had not been traveling, hadn't been traveling, Before modern aircraft became highly efficient, engineers _____________ ways to reduce their weight and fuel consumption. (explore), had been exploring, Before the first jet aircraft entered commercial service, engineers _____________ reliable jet engines for civilian aviation. (not / develop), had not been developing, hadn't been developing, Before Charles Lindbergh completed his historic transatlantic flight, most pilots _____________ nonstop flights across the Atlantic for such a long period. (not / attempt), had not been attempting, hadn't been attempting, Before modern aircraft became widespread, airlines _____________ advanced navigation systems for long-distance flights. (not / use), had not been using, hadn't been using

Past Perfect Continuous ✈️

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