The question raised in the first paragraph is one

单项选择题

Can Buildings Be Designed to Resist Terrorist Attack
In the aftermath of the terrorist attack on the World Trade Center, structural engineers are trying hard to solve a question that a month ago would have been completely unthinkable. Can building be designed to withstand catastrophic blasts inflicted by terrorists
Ten days after the terrorist attacks on the twin towers, structural engineers from the University at Buffalo and the Multidisciplinary Center for Earthquake Engineering Research (MCEER) headquartered at UB traveled to ground zero as part of a project funded by the National Science Foundation. Visiting the site as part of an MCEER reconnaissance visit, they spent two days beginning the task of formulating ideas about how to design such structures and searching for clues on how to do so in buildings that were damaged, but still are standing.
"Our objective in visiting ground zero was to go and look at the buildings surrounding the World Trade Center, those buildings that are still standing, but that sustained damage," said M. Bruneau, Ph.D. " Our immediate hope is that we can develop a better understanding as to why those buildings remain standing, while our long-term goal is to see whether earthquake engineering technologies can be married to existing technologies to achieve enhanced performance of Buildings in the event of terrorist attacks." he added.
Photographs taken by the investigators demonstrate in startling detail the monumental damage inflicted on the World Trade Center towers and buildings in the vicinity. One building a block away from the towers remains standing, but was badly damaged. "This building is many meters away from the World Trade Center and yet we see a column there that used to be part of that building", explained A. Whittaker, Ph. D. "The column became a missile that shot across the road, through the window and through the floor."
The visit to the area also revealed some surprises, according to the engineers. For example, the floor framing systems in one of the adjacent buildings was quite rugged, allowing floors that were pierced by tons of falling debris to remain intact. "Highly redundant ductile framing systems may provide a simple, but robust strategy for blast resistance." he added. Other strategies may include providing alternate paths for gravity loads in the event that a load-bearing column fails." We also need a better understanding of the mechanism of collapse" , said A. Whittaker. "We need to find out what causes a building to collapse and how you can predict it."
A. Reinhorn, Ph.D. noted that "earthquake shaking has led to the collapse of many buildings in the past. It induces dynamic response and extremely high stresses and deformations in structural components. Solutions developed for earthquake-resistant design may be directly applicable to blast engineering and terrorist-resistant design. Part of our mission now at UB is to transfer these solutions and to develop new ones where none exist at present."

The question raised in the first paragraph is one ______.

A.that was asked by structural engineers a month ago.
B.that is too difficult for structural engineers to answer even now.
C.that was never thought of before the terrorist attack.
D.that terrorists are eager to find a solution to.