When you forget entire experiences, he says, that's "a red flag that something more serious may be involved."
2018年6月四級(jí)真題（第二套）閱讀 Section C
More than a century has passed since explorers raced to plant their flags at the bottom of the world, and for decades to come this continent is supposed to be protected as a scientific preserve, shielded from intrusions like military activities and mining.
出自-2016年12月閱讀原文
Because their behaviors are not usually seen as a red flag, these young people have been dubbed the invisible risk group by the study's authors.