[D41] It has been proved ------ eating vegetables in childho

答案的确是that,估计是楼主打错答案了。翻译：已经证实,儿童时期食用蔬菜有助于保护你免受后期生活中重大疾病的侵扰。1。此句中,it为句子的形式主语,而proved后面的从句才是该句的真正主语,即为主语从句。该主语从句中,eating vegetables in childhood helps to protect you against serious illness in later life并不缺少任何成分,所以只需用that引导即可。2。if/because都不能用于引导主语从句,排除AB；when表示从句缺少时间状语,what表明从句缺少表sth的主语/宾语等,都不对。