An envelope is a flat paper container used to send a letter.

信封指平板纸容器，用来寄信。

Now you buy milk and other products in plastic bottles or paper containers.

现在你买用塑料瓶子或者纸容器装的牛奶和其他产品。

Now you buy milk and other products in plastic bottles or paper containers because of the high cost of disposing of these things in landfills.

现在你买装在塑料瓶或纸容器里的牛奶和其他产品 因为在垃圾填埋场处理这些东西的成本很高。