US scientists are helping students figure out how to farm on Mars， much like astronaut Mark Watney， played by Matt Damon， attempts in the movie " The Martian".

Washington State University （WSU） physicist Michael Allen and the University of Idaho （UI） food scientist Helen Joyner teamed up to explore the （1） c .

"Congratulations！ You are leaving Earth forever，" the case study begins.

"You are selected to be part of a mining colony of 100 people located on the （A） p Mars. Before you head to Mars， however， you need to figure out how to feed yourself and your （2） c

once you are there，" the study said.

The task is similar to that of Watney， who must grow （B） f in an artificial habitat after he is separated from his mission crew in a Martian windstorm， "Mars will come to fear my botany powers，" he boasts.

Allen and Joyner have students identify potential challenges to producing crops indefinitely and develop criteria for selecting crops. Students then use a scoring system to select three optimal foods.

In some 30 trial runs with （3） s and teachers， "no two people have ever gotten the same answer，" said Allen.

"One particular challenge is that scientists have little idea of what Martian soil is actually like， " he said. Probes have detected little carbon， the central （C） e to life as we know it， or nitrogen， which is needed to make protein. Water is also likely to react with peroxides in the soil， bubbling off as gas.

Like real （D） a ， the tabletop astronauts are limited in what they can bring， so they won't have a lot of （4） t to farm with.

"You are starting with nothing. If I had to eat a single food for the rest of my life， could I do it？" Joyner said.

" But in a sense， （5） f and dining on the Red Planet is beside the point，" Allen said.

"I'm not teaching about growing food on Mars. I'm teaching about living with choices. I'm teaching about （E） p solving，" he said.

（A， B， C， D， E FOR CROSS， 1， 2， 3， 4， 5 FOR DOWN. The first letters of the absents were given.）