题目

Guests arriving at the Aloft Hotel in Manhattan or one in Silicon Valley will soon be able to do something hotels have dreamed about offering for years: walk past the check-in desk and enter their rooms by using a smartphone as a room key. The boutique hotel brand from Starwood to Hotels & Resorts Worldwide Inc. plans to offer this feature at two hotels before the end of the quarter.Starwood officials are hoping this will be one of the biggest technological changes in the industry since free Wi-Fi. “We believe this will become the new standard for how people will want to enter a hotel.已知向量均为单位向量，若它们的夹角是60°，则等于     （    ）     A． B． C． D．4