I'm Alan. The weekend just ended. Yesterday I went to visit the museum. It is about 3 kilometers away from my home. So I decided to go there by bike, I set off at half past eight. At the museum I saw many photos and other things. I learned a lot. There were also a lot of children with their parents，students with their teachers and soldiers. At eleven o'clock, I left the museum for home. I had a wonderful time yesterday.

阅读短文，回答下列问题。

则下列说法正确的是（   ）

给甲乙丙三人验血型，先用A型标准血清检验，结果甲乙两人血液发生凝集反应；再用B型标准血清检验，结果乙丙两人血液发生凝集反应．那么，三人的血型依次是（    ）

比较﹣ $\frac{1}{3}$ ，﹣ $\frac{1}{4}$ ， $\frac{1}{6}$ 的大小，结果正确的是（   ）