《郑人买履》给了我们这样的启示:____。

①In order to protect our environment, we can't freely cut trees without the government's ____(允许)．

②There is no ____ (通路) to the street through that door.

③Humor is a more effective ____(防御) than violence(暴力)．

④Now that you are a college student, you should learn to be ____ (独立的)of your parents' help.

⑤Can you give me a ____(明确的)answer by tomorrow?

⑥With his new method, the time of the project will be ____ (缩短)．

⑦They brought the piano ____(斜着地) through the front door.

下列物质与水混合，在室温时难以形成饱和溶液的是（）