单项选择题 （ ）is a computer technology that headsets,sometimes in combination with physical spaces or multi-projected environments,to generate realisitic images,sounds and other sensations that simulate a user’s physical presence in a virtual or imaginary environment.

单项选择题 （ ）：a cloud service,allied to the set of business terms under which the cloud service is offered.

单项选择题 同时抛掷3枚均匀的硬币，恰好有两枚正面向上的概率为（ ）。