根据提示，把下列句子补充完整。

1. Where does the ___________ (雨) come from?

    It comes from the ___________ (云).

2. Where does the ___________ (水蒸气) come from?

    It comes from the ___________ (水) in the ___________ (小河).

3. First, we have the ___________ (种子).

4. What are you going to do ___________ (今天下午)?  

    I'm going to ___________ (种植) flower seeds in our ___________ (花园).

5. It's ___________ (简单的). Put the seeds in the ___________ (土).

一般砂型铸造技术的浇注系统结构主要由浇口杯，直浇道，横浇道，内浇道组成。