设<img src="https://static.zxtiku.com/wangke/imgs/topic/b465a1f0be323f71fa40c09740231d63.jpg"/>都是随机变量的分布函数，<img src="https://static.zxtiku.com/wangke/imgs/topic/6186122da8652fa0b875a2daf7fbd6cf.jpg"/>是相应的概率密度，则( )．<br /> <br /> A、<img src="https://static.zxtiku.com/wangke/imgs/topic/7979522fb5a97ff4bf8e7ae9cb6518fe.jpg"/>是概率密度<br /> B、<img src="https://static.zxtiku.com/wangke/imgs/topic/1155766f67ac6f80440c4f86af232305.jpg"/>是概率密度<br /> C、<img src="https://static.zxtiku.com/wangke/imgs/topic/414df059dd8c188a399cd4361d7281be.jpg"/>是分布函数<br /> D、<img src="https://static.zxtiku.com/wangke/imgs/topic/a0e3c04dabc711f3f516e48a3b395c64.jpg"/>是分布函数