Which of the following statements is incorrect in regard to stones in the gallbladder ?

• A. 10% of gallstones are radio-opaque
• B. A mucocele of the gallbladder is caused by a stone impacted in Hartmann's pouch
• C. Pigment stones are due to increase excretion of conjugated bilirubin
• D. Are considered a risk factor for the development of gallbaldder carcinoma