House of Porridge
    Welcome to Clark's Porridge House. We have different kinds of porridge. We have meat porridge, vegetable porridge. And fruit porridge is our special, it is only RMB 4 yuan for one bowl. A bowl of meat is RMB 5 yuan. Vegetable porridge is RMB 3 yuan for one bowl, but RMB 5 yuan for two. We have thin pancakes, too. They are RMB 5 yuan for ten. Come and taste the delicious food here. If you are too busy to come, make a telephone call to us and we can send the food to you in 20 minutes.
阅读以上信息，完成下面的句子，每空一词。

$\frac{3}{5}$ 的分母扩大了3倍后，要使分数的大小不变，分子应加上____。

下列图案中，是中心对称图形但不是轴对称图形的是（　　）