Which Is True Regarding Caries Detection

Which is true regarding caries detection?

A) Research shows that a sharp explorer stick is the most effective technique for diagnosing occlusal decay.
B) Radiographs are effective for diagnosing occlusal and proximal caries.
C) A dark discoloration is always caries.
D) Several types of devices have been developed that can provide a higher level of discrimination than an explorer in the diagnosis of dental caries.