It sounds very easy while wishing out such lists.
Even few days back, it sounded very easy to connect China to US via Alaska.
But in technical manner,
it doesn't sound so easy in reality.
Euro...
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Tunnel was a hectic challenge in the those periods. the Tunnel Digger was bought all the way from other nation. Safety was more imp, as it was deeper in the sea.
Talking of a road / rail on sea, specially vast open sea, its a danger n most challenging for almost 10-20+ km.
Compromising with Nature is like putting hand in Lion's mouth.
Connecting China - US isn't an easy task as it has pass thru world's most dangerous zone aka called the Pacific Ring of Fire.
One slight difference in geo issue, it will cost a lot amount to the investors, danger to human lives n infrastructure.
Even though the project will cost over billions, but in front of nature, its just like pieces of sand or rocks to b crumbled.
One Tsunami is of 20-50 meters is enough to wipe out the bridge if suddenly the plates beneath us moves in either direction and history might repeat.
Natural disaster don't warn before they come.
It reminds me of the famous quote
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"The arrogance of men is thinking nature is in their control and not the other way around. Let them fight."
Dr. Ichiro Serizawa