主语Researchers in the US,谓语found, 第一个that是连接词引导宾语从句（that on contrary to the popular view that having children would reduce a woman’s brainpower, it actually can improve her lifelong mental ability.）,第二个that引导同位语从句（that having children would reduce a woman’s brainpower）对view（观点）进行解析和说明,指示代词it指代前面的having children.