This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Ophthalmology
What percent of retinoblastomas are Bilateral? 
Select and explain. 
A. 10, B. 20, C. 30, D. 50
C: 30
Answer: C: 30 
Explanation: Retinoblastoma is the most common primary malignant intraocular tumor in children, occurring in approximately one of 20000 bihs. In 30% of all cases, it is bilateral.