Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the questions from 3 to 7.

As you know, the burning of fossil fuels like coal, oil and natural gas emit greenhouse gases. That is why environmentalists insist that we use clean, renewable energy sources. Wave energy, produced by ocean surface waves, is both eco-friendly and cost-efficient. Research has suggested that ocean wave power could make a major contribution to the world's energy resources. Scientists claim that using 1% of wave energy can provide the equivalent of 500 times the world energy consumption. With 70% of the earth's surface covered with water, wave energy is undoubtedly a valuable source of green energy.

However, there is the challenge of converting wave power into energy and transmitting it to shore. Building and operating wave power stations in the ocean is far more expensive and difficult than on land. Also, salt water is a very hostile environment to devices. They go rusty easily and cannot last as long as those on shore. Sea waves make energy harvesting even harder by moving up and down most of the time.

Viet Nam has a long coastline with great potential for producing wave energy. Hopefully, advancements in renewable energy technology will soon allow us to exploit wave energy effectively and efficiently.

Which best serves as the title for the passage?

• A. 
  The cost of wave energy
• B. 
  Wave energy – source of clean energy for future
• C. 
  The limitation of fossil fuels
• D. 
  Advancements in energy technology