题目

    A new study by the Pew Research Center shows that the number of dads who choose to stay home and care for their children and families has quadrupled (成为四倍) over the past 25 years. Can social and economic factors explain the change?     Make no mistake; fathers who are the primary caregiver for their children are far from the norm. In fact, they are only 16% of all stay-at-home parents.but that number is up from 10% since 1989. When pew started analyzing data. The steady growth since then suggests that these numbers represent a growing trend.     “It’s up from 　　细菌、真菌等生物的分类，只能以菌落大小为依据。 (　　)