服务速度变慢的原因有：如今菜单上的选择更多了，而且产品本身也更复杂，准备时间更长。
Among the reasons for the slower service, today there are more choices on the menu, and the products themselves are more complex and take longer to prepare.
然而，男孩比女孩更倾向于玩复杂的谜题，而且男孩的父母在玩谜题时比女孩的父母提供更多的空间语言，也更活跃。
However, boys tended to play with more complex puzzles than girls, and the parents of boys provided more spatial language and were more active during puzzle play than parents of girls.
由于这些数据有时相互矛盾，而且其机制也不时发生明显的变化，这些研究变得复杂起来。
The studies are complicated by the fact that the data are sometimes contradictory and the mechanisms apparently change from time to time.
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