2007 AMC 10B Problem 5

Writing the statements as implications, being a Crup implies being a Dramp, a Dramp implies being an Arog, and an Arog implies being a Braf: $C\Rightarrow D\Rightarrow A\Rightarrow B.$ So every Crup is a Dramp, an Arog, and a Braf. The only listed statement guaranteed true is that all Crups are Arogs and Brafs. Thus, the correct answer is D.