分式 $\frac{3}{{\text{a}}^2\text{b}}$ ，﹣ $\frac{1}{{\text{2ac}}^2}$ ， $\frac{2}{{\text{3b}}^2\text{c}}$ 的最简公分母是____．

     Mary likes dogs very much. She has a pug-dog. It is white. It has big eyes and ears. It is small but it is cute and beautiful.
    Every morning, the dog eats some bread and meat. They are the dog's favorite food. When Mary goes to school, the dog always waits for(等待) her at the gate. When she comes back home, the dog follows her here and there. When Mary does her homework, it lies(卧) near her feet. When Mary watches TV, the dog sits on the sofa near her. When Mary goes to bed, the dog lies its bed next to Mary’s. in the evening, they often run and play in the yard (院子). They are really good friends. 
根据短文内容，选择正确答案。