The correct answer is: D. 1900s.
The first hang glider was flown in 1902 by Otto Lilienthal in Germany. He was a pioneer in aviation and made over 2,000 successful flights in gliders. His work was an important step in the development of heavier-than-air flight.
The other options are incorrect because they are too early. Hang gliding is a relatively new sport, and it was not invented until the early 1900s.
A. 1600s: This is too early. The first hang gliders were not invented until the early 1900s.
B. 1700s: This is still too early. The first hang gliders were not invented until the early 1900s.
C. 1800s: This is getting closer, but it is still too early. The first hang gliders were not invented until the early 1900s.
D. 1900s: This is the correct answer. The first hang gliders were invented in the early 1900s.