答:表状态的介词in, 此时表示某事正在进行之中的。例如: The house is in repair. = The house is being repaired now.
表示状态的介词on, 表示某人正处于某种状态,或者某事正在进行中。例如: He is on holiday. (= He is having/ taking a holiday now. )
介词at 表示某人/某物正处于某种的状态中。例如: He is at rest in the bed. ( = He is having a rest in the bed. )