47 What does “Such changes” refer to in the second paragraph?
(A) Having elevator-dedicated emergency power systems.
(B) Improving the software and sensing systems.
(C) Installing waterproof elevator components.
(D) Using remote control operations.

       The elevators are the primary means of vertical豎直 transportation in most high-rise buildings and potentially can play a vital重要 role in the event（重大或不尋常）事情 of an emergency, such as a fire. The dominant主導 practice around the world, however, is to discourage the use of elevators during a fire. The major reason for this practice is the unpredictability不可預測性 of the condition of the emergency and the danger of entrapping誘捕; passengers as well as rescue workers (e.g. firefighters) in the elevator.  

      To safeguard the use of elevators in a fire emergency, the US National Institute of Standard and Technology (NIST) is working with the elevator industry to develop new elevators that function during fires. The new elevators are designed to be used both as a rescue vehicle, carrying firefighters to the site地點 of the blaze熊熊燃燒, and as a secondary method (after stairwells樓梯井) for evacuating building occupants居住者, 佔有人. NIST is investigating software and sensing systems that can adapt to changing smoke and heat conditions so that the elevators can maintain safe and reliable可信賴 operation during fire emergencies. Such changes could also allow elevators to be operated with remote遙遠 control from the ground floor during fires, thus freeing urgently緊急 needed firefighters from elevator operation duties. NIST is also testing more reliable elevator-dedicated盡心盡力 emergency power systems and waterproof elevator components成分；零件 to be used in the new generation of elevators.

      Besides hardware硬體 and software improvements改進，改善, NIST also incorporates包含 its expertise專門技能（知識）in virtual reality  simulation類比，模仿 into the making of the new elevators. Virtual reality simulations help test scenarios劇情 for coordinating協調 firefighting activities, and for elevator and stairway樓梯 vacuation撤空. By including elevators into its graphic清楚、形象 computer models, NIST will help fire safety experts identify the most effective operational procedures for specific fire conditions. Furthermore此外，而且, NIST fire researchers hope to collaborate合作 on emergency elevator operations standards with colleagues from around the world. Global standardizetion使標準化 should reduce減少 confusion困惑，糊塗 during an emergency, enabling people to take evacuation actions with confidence.