be to ,be able to句的否定式和疑问式是什么,请举例

用be to ＋动词原形表示职责、义务、意图、约定、可能性等.如：x0d①You are to be back by nine o'clock．到九点你就得回来.x0d②We are to meet at the schoolgate．我们要在校门口见面.x0d注意：be to do还可以表示注定要发生某事.如：x0d③He was later to be a famous musician．他注定日后要成为一位著名的音乐家.x0d否定:not to be,x0d疑问:be sb to do用be able to表示能力,译能