分析这句话的语法成分 Scientists say they have strong evidence that a b

Scientists (主语）say （谓语）（they have strong evidence that a biological problem could explain why some babies die suddenly in their sleep.宾语从句）
that a biological problem could explain why some babies die suddenly in their sleep.是evidence的定语从句
why some babies die suddenly 是explain的宾从

that引导的是一个定语从句,该从句中包括一个"why"引导的宾语从句,其中,evidence作为定语从句的先行词,that是定语从句的引导词.
判断定语丛句和宾语从句的简单方法:一般名词后跟的是定语从句,用于修饰前面的名词,动词后一般跟宾语从句用于补充解释前面动词所要表达的内容....