第 48 至 51 題為題組         Demolition is the tearing-down of buildings and other structures. You can level a five-story buildingeasily with excavators and wrecking balls, but when you need to bring down a 20-story skyscraper,explosive demolition is the preferred method for safely demolishing the huge structure.        In order to demolish a building safely, blasters must map out a careful plan ahead of time. The firststep is to examine architectural blueprints of the building to determine how the building is put together.Next, the blaster crew tours the building, jotting down notes about the support structure on each floor.Once they have gathered all the data they need, the blasters devise a plan of attack. They decide whatexplosives to use, where to position them in the building, and how to time their explosions.             Generally speaking, blasters will explode the major support columns on the lower floors first andthen on a few upper stories. In a 20-story building, the blasters might blow the columns on the first and  second floor, as well as the 12th and 15th floors. In most cases, blowing the support structures on thelower floors is sufficient for collapsing the building, but loading explosives on upper floors helps breakthe building material into smaller pieces as it falls. This makes for easier cleanup following the blast. Themain challenge in bringing a building down is controlling the direction in which it falls. To topple thebuilding towards the north, the blasters set off explosives on the north side of the building first. Bycontrolling the way it collapses, a blasting crew will be able to tumble the building over on one side, intoa parking lot or other open area. This sort of blast is the easiest to execute, and it is generally the safestway to go.
【題組】48. What do the blasters need to do in preparing for the demolition of a building, according to thepassage?
(A) Study the structure of the building.
(B) Hire an experienced tour guide.
(C) Make a miniature of the building.
(D) Consult the original architect.