This round we asked: What mystery would you love to see solved?
Michelle Fasching, 15, Maryknoll Convent School
I would love to see the mystery behind the creation of Stonehenge solved. This gigantic ring of stones found in southwestern England has been the centre of countless myths and conspiracies. Some think it used to be a temple for the ancient Egyptians, while others believed it was the work of Merlin, the wizard.
According to BBC TV's Doctor Who, Stonehenge was placed there by inter-galactic armies (basically a bunch of different aliens), to mark the spot of the Pandorica, or, as we Earthlings prefer to call it, Pandora's Box. This is my favourite theory so far.
Compared with the comparatively unexciting theory of Stonehenge being built by ancient humans, I prefer to believe the alien theory, as it is way more fun. I really do think Stonehenge deserves this rather outrageous solution.
The myths behind its construction range from ancient civilisations to magic, and researching this, I was able to examine a lot of different beliefs, scoffing at some, and marvelling at others.
By solving this mystery, humankind would probably also unveil a few other wonderful things - be it life on somewhere other than Earth or a new source of energy. And I probably would get to prove to all my friends that I was right all along.
Thomas Cheung Chak-wang, 17, Shatin Tsung Tsin Secondary School
There are many mysteries in our world. But, as a science-class student, please let me to choose something more scientific. What would happen if we could travel faster than light speed?
Some say we would enter an alternate universe after we shatter the speed of light. But what could we do in this alternate universe? Could we meet fictional scientist William Bell, of TV's Fringe, in the World Trade Centre? Or could we cast a spell with our wands bought from Ollivanders?
Some say we could go back in time. Could we be like Christopher Reeve, in the film Somewhere in Time, and meet our true love 70 years ago? Could we travel with Doc, in Back to the Future, in a DeLorean DMC-12?
Some people say we could invent a warp drive. We could explore deep space. We could meet aliens! "Calling occupants of interplanetary craft!"
With the mystery solved, we may be able to invent a time machine. We could solve other mysteries with that.
We could travel to 1962 to investigate the death of former president John F. Kennedy, or 1947, to witness the crash of the UFO in Roswell, New Mexico.
Finally, we could go into the future to see the end of the world.
Lexie Lee Hoi-ching, 16, Hioe Tjo Yoeng College
I'm sure one of the top 10 most famous unsolved mysteries would be the appearance of unexplained crop circles. Crop circles are when large circular areas of crops, like wheat or corn, are flattened and form distinct patterns.
In the past four decades, more than 10,000 crop circles have been reported in 26 countries. What amuses me the most is that 90 per cent popped up in southern England. What is so exceptional about southern England? Is it the base of aliens, or are the people there wizards?
I've been racking my brain to work out what power is hidden in those patterns. I firmly believe that there are close links between crop circles, human civilisation and the supernatural.
There have been various explanations for these crop circles. Some say they are caused by paranormal forces, while others say animals, the weather or even humans playing pranks are to blame. Whatever the cause, I think these circles convey a crucial message for the Earth. After the epic failure of the Mayan prediction, the crop circles might give us a new idea when the world will end. And if we are lucky, the aliens who created them might save us!
Vanessa Sin, 15, St Paul's Convent School
On one hand, we believe that life is full of trillions of riddles with answers blowing in the wind. There are unsolvable questions out there with explanations that exist only in the wildest reaches of our imagination.
On the other hand, we humans possess far more knowledge than we think we do. For instance, the average human does not know how snails reproduce. Yet, there are scientists out there happy to explain the whole process down to the smallest detail.
However, to me, the greatest mystery of all time is not how the universe was created, nor is it why girls love to gossip so much. It is why mothers love their children.
A teacher once told me, "God gave mothers some kind of power to love their children, no matter what". That hit me really hard because I was having a quarrel with my mum at that time, and was, of course, going through post-argument depression.
It reminded me of the countless times the woman who gave birth to me was there when I thought the world had given up on me, reassuring me with her warmth. Basically, my mother is my world.
This why I would love to solve this mystery - the mystery of motherly love. Because one day, I hope to be as great a mother as my mother is to me.