根据课文内容填空

 time, some plants develop features which help them to  in particular conditions. Plants with helpful features are more likely to survive and . Plants without these features often die . This process is called natural .

Countries around the are spending billions of dollars and lots of time on various space missions, whether to Mars or other planets much further away. Some people argue that we should stop wasting time and money space., we should feed the world's poor and find immediate solutions to other problems, such as pollution and diseases. However, others feel this is a view which fails to realise how exploring space helps us.