Answer:
I believe that it's D (but maybe A)
Explanation:
Please remember I could be wrong, however, what made me think it's A was:
In 2016, Browning set out to build a sleek suit that would allow a human to fly. He knew his suit would need to produce an upward force stronger than the force of gravity pulling him to Earth. - Cause
Browning started by collecting several jet engines. - Effect
However, it isn't that great of an answer, for one it isn't really a cause nor an effect, for one it's talking about how he wanted to make something, but he needed something else to make it work, later making the problem have a solution by. But, the reason why I think it's mainly D is because:
He KNEW his suit would need to produce an upward force stronger than the force of gravity pulling him to Earth. - Problem
He started by collecting several jet engines ~ these devices can blow out air, creating a pushing force called thrust, testing the engines, later helping and creating an upward force called 'lift'. - Solution
