They are trying to use 3D printers to print food that is both and good for us． （美味的）
Greenhouse gases are to the environment． （harm）
There're many rocks in unusual shapes﹣ some hang down， and others upwards． （指向）
Tan Dun's music Water， which is full of the sounds of nature， is listening to．（值得）
The temperature in our hometown usually drops zero in winter． （在……以下）
Follow these small ， and you can make a big difference to the Earth．（步骤）