Question

as proved by the transatlantic flights of lindbergh and earhart, postwar airplanes were engineered to fly for greater distances with heavier loads at lower altitudes at higher altitudes

Explanation:

The transatlantic flights of Lindbergh and Earhart demonstrated long - distance flight capabilities. Post - war airplanes, building on this, were engineered to fly for greater distances. The other options (heavier loads, lower altitudes, higher altitudes) are not directly related to the context of transatlantic flights which emphasize distance.

Answer:

for greater distances