河马的皮脂腺在夏天能分泌出黏液，抵挡紫外线，这种黏液呈（）
A、无色
B、绿色
C、黄色
D、红色
参考答案：A
根据图片提示完成对话。
A: Where does the 1____________ come from?
B: It comes from the 2____________ .
A: Where does the cloud come from?
B: It comes from the 3____________ .
A: Where does the vapour come from?
B: It comes from the water in the 4____________ .
A: How can the water become vapour?
B: The 5____________ shines and the water becomes vapour.
A: Oh, I see.
有四个数：2，3，0，7，先要添加一个数，使它们的平均数增加1，则添加的数是______．
come from? 
. 
. 
. 
shines and the water becomes vapour.