Part A
The answer is A: Like Armstrong's Moon landing, the launch of the first Robonaut aboard the Discovery represents a historic breakthrough in space exploration.
The author is drawing a parallel between the significance of Neil Armstrong's historic Moon landing and the launch of Robonaut 2 (R2), suggesting that both events are monumental achievements in the context of exploring and understanding space.
Part B
The piece of evidence that best supports the answer to Part A is A, which states: ". . . our challenge has been to build machines with dexterity that exceeds that of a suited astronaut." (paragraph 1).
This evidence underscores the aim of Robonauts to match or surpass human capabilities, linking their significance to advancements in space exploration, much like the historic nature of the Moon landing.