People who get less than six hours of sleep per night have an increased _____ of dying early．

A．custom

B．practice

C．disadvantage

D．risk

下列各组离子一定能大量共存的是 [ ]

A．在含大量Fe³⁺的溶液中：

B．在强碱性溶液中：

C．在pH=1的溶液中：

D．在无色透明溶液中：