Steve Robinson went for a walk yesterday m

题目：

Steve Robinson went for a walk yesterday morning with tens of millions of people watching. A walk in space. What made his

sojourn

so different from those of the hundreds of other astronauts who have floated around shuttles for more than 20 years is that the very future of the nation’s manned space program may rest on his success.
In the wake of the Columbia disaster 30 months ago, and amid questions about NASA’s commitment to a safety-first culture, Robinson tested what accounts to the repair kits to help astronauts survive damage from debris during lift-off or in orbit. Apparently, the repairs went well.
How well, however, and whether the spacecraft sustained damage from foam insulation as it rose from Kennedy Space Center, won’t be known until Discovery completes its super-heated descent through the atmosphere and touches down.
What is known now is that NASA allowed Discovery to fly despite internal questions about whether NASA had done enough to address safety issues raised inside and outside the agency. That’s disquieting. Space flight is dangerous; it can never be as safe as, say, a flight in a jetliner. But every investigation following both the Challenger and Columbia tragedies cited a culture that did not put safety first.
Yes, NASA has made progress. Robinson’s repair walk is evidence of that. For now, let’s hope for the best for the seven brave astronauts as, amazingly, they do their jobs.

Which of the following is NOT cited by the author in his criticism of NASA’s neglect of safety

A．NASA’s allowing Discovery to fly in spite of questions about safety.

B．Launching the spacecraft from Kennedy Space Center.

C．The Columbia disaster 30 months ago．

D．The explosion of Challenger．