【单选题】_____ is well-known to all that the 2016 Olympic Games will be held in Rio de Janeiro, Brazil. [ ]
【单选题】is known to us is that the 2016 Olympic Games will be held in Rio de Janeiro, Brazil.
【单选题】_______is known to us all is that the 2016 Olympic Games will take place in Rio de Janeiro. [ ]
【简答题】每个电压中,开关元件多次通断,使电压斩波成多个 ____