According to Sophia’s dad, what does the excessive use of non-renewable sources cause?

Read the passage. Circle the best answer A, B, or C to each of the questions.

If you are a big fan of Doraemon, a Japanese cartoon series, you will realise that there are some magic gadgets that can transport people from one place to another in a super modern way. They are imaginary products that reflect people’s desire to invent future means of transport. One of the most popular ones is the bamboo-copter. It has a semi spherical base connected with spinning rooters by a thin shaft. Just putting it on any part of the body, Doraemon and his friends can fly anywhere they want by just thinking. It looks small but can carry a heavy body. Although it runs on batteries, it doesn’t pollute the environment. However, sometimes users can have a big problem if the battery is flat, especially when they cross a vast ocean or desert.     

What is the passage mainly about?