31，Space travel will become cheaper in the future

32，We can use machines instead of human beings

We can use machines to replace human beings

33, If governments raise the price of petrol, there will be less cars on the road

If governments increase the price of petrol, there will be fewer cars on the road

34, Students are harder to earn a high grade at school because the intense competition

Students are unlikely to earn a high grade at school because of the intense competition

It is hard for students to earn a high grande at school because of the intense competition

35, Technology makes our life much simpler and much happier then before

Technology makes our life simpler and happier then before

36, Everyone needs to take actions to protect the environment

37, Reducing the use of fossil fuels are beneficial to protect the environment

Reducing the use of fossil fuels is beneficial to protecting the environment