单项选择题
A.createB.just(T...)C.fromD.Observer
A.Subscriber.getB.new SubscriberC.Subscriber.buildD.SubSubscriber.getInstance
A.观察者B.被观察者C.事件D.监听
A.onNextB.onErrorC.onStartD.unsubscribe
A.ObserverB.SubscriberC.onNextD.onCompleted
A.onErrorB.onNextC.onCompletedD.OnClick
A.ObservableB.subscribe()C.事件D.Observer
A.ObserverB.ObservableC.subscribeD.事件