Answer:
D. simple
Step-by-step explanation:
As used in paragraph 2, the best antonym for complex is simple.
Complex is known to be a system of different things which are linked or connected in a close or complicated way. Antonym means the opposite of something. So, the opposite of complex as used in paragraph 2 is "simple".
From the passage, the narrator further explained why he said the Ferris Wheel is complex. He revealed that the way the wheel works is complicated. So, the antonym is simple. Option D is correct answer.