at the age of adv.在...岁 She graduated from the high school at the age of 18. by the time是过去完成时的标志,看见这个标志,就一定要用过去完成时. J-Lo Wants to Be Pregnant by the Time of Her 40th Birthday in July at that time:是指在过去某段特定的时间,是特指 adv.在那时 Where were you at that time?你当时在哪里呢?
