This round we asked: Given unlimited resources, what scientific or medical problem would you investigate?

Nicholas Chu Weng-lam, 16, Sing Yin Secondary School

What time is it? According to the famous Doomsday Clock, it's now five minutes to midnight. If the clock strikes 12, we are all doomed.

But don't panic! This is just a symbolic clock that tells us how close we are to nuclear war or tragedy.

Nuclear energy is vital. Fossil fuels like coal and petroleum will eventually run out. Renewable energy sources such as solar, water and wind power have their limitations.

After the Fukushima nuclear plant disaster, people have started paying attention to the dangers of nuclear power again. Yet global demand for energy is constantly growing. Many territorial disputes between nations stem from the scarcity of natural resources.

So what to do? Science can help. A real estate company in Sweden has found a way to harness body heat as an energy source. Thousands of commuters pass through Stockholm's Central Station every day. Their excess body heat is collected by the ventilation system to generate electricity. Think about that!

The system then provides hot water to keep nearby office blocks warm in winter.

This method is not only environmentally friendly, but it also reduces the energy costs of the buildings in the neighbourhood.

That is one way to go forward.

Vivian Li Wan-yi, 16, Wa Ying College

If I had unlimited resources, I would dedicate myself to curing Alzheimer's disease. As populations age, the disease becomes more and more common.

And the disease can affect even young people - because their elderly loved ones suffer from it. Those who suffer from Alzheimer's need good care, and usually that responsibility falls on their children. It's a huge burden especially for young couples with small children.

My grandma contracted Alzheimer's when I was 14 years old. She became gradually forgetful until one day she no longer remembered who I was. She never recovered her memory. I was so sad.

We need to find a cure for this terrible disease.

Thomas Lee Ka-chun, 16, Sing Yin Secondary School

It hasn't been long since we last saw a banner with the words "No more carbon dioxide!" on the street.

But cutting down on our emissions is pretty hard because of all those cars and electrical appliances we have.

So why don't we invent a machine that can consume carbon dioxide on our behalf instead?

We need energy - and plenty of it - to have a better life. Yet many green groups have voiced concerns about the negative consequences of our economic prosperity.

As the economy grows, the environment suffers, they say.

That's where my machine comes in. It would turn carbon dioxide into clean and pure oxygen, the way trees and plants do.

Then again, considering the huge pollution problem we have, we would need a pretty big machine.