24.Does your father often go to work-----B-----?A.by a train

24.Does your father often go to work_____B_____?A.by a train B.on a train C.take a train24.Does your father often go to work_____B_____?A.by a train B.on a train C.take a train D.catch a train这道题为什么选B,by 不是放在句尾么?at the age of 和when的区别是什么?它们分别在句子的哪个位置?