从句是不是就是修饰主语的句子
three signs that indicate a person is suffering from a panic attack rather than a heart attack
三种意味着一个人是患有惊恐症而不是心脏病的迹象在这个带有定语从句的名词短语中：
signs是：被修饰的名词；
that是：关系词；
that indicate a person is suffering from a panic attack rather than a heart attack是定语从句