This ticket machine is broken. 这台售票机坏了。 (1) 改为疑问句  —> Is this ticket machine broken? (2) 句子开头加 I wonder if 我想知道是不是……/ 我怀疑是否…… —> I wonder if this ticket machine is broken. (3) 改为以 someone “有人/某个人”为主语的主动式句子，时态为过去时 —> Someone broke this ticket machine. 有人把这台售票机弄坏了。 There are no seats on the bus. 公共汽车上没有空位。 (1) 将 no 改为 some 的肯定句 —> There are some seats on the bus. (2) 改为疑问句 —> Are there no seats on the bus? 公共汽车上没有空位吗？/       Are there any seats on the bus? 公共汽车上有空位吗？ (3) 改为用 must “应该……”做助动词的句子 —> There must be no seats on the bus.