1. The sites shield themselves from search engines, so they do not pop up in response to online searches for the brands they offer. 这些网站避开了搜索引擎，所以若在线搜索他们所卖的品牌时，他们的网站是不会出现的。
2. As noted above, indifferent relationships may not always be the most helpful approach in resolving some of the issues that pop up at work. 如上所述，在解决工作中出现的一些问题时，冷淡的关系并不总是最有用的方法。
3. The same narrative units—gathering armies, heroic shields, challenges between rivals—pop up again and again, only with different characters and different circumstances. 军队集结、英勇抵抗、对手间的争斗，此类叙事单元不断重复出现，只有角色和场景发生变化。
4. Colds mutate even while they're infecting you, and new strains pop up so often that by the time drug-makers create a vaccine against one variation, the serum is already out of date. 即使在感染你的时候，感冒病毒也会发生变异，而且新的病毒毒株经常出现，以至于当制药商研制出针对其中一种变异的疫苗时，血清已经过时了。
