Answer:
1
Explanation:
The rest are wrong b/c it helped <em>expand</em> China rather than isolate it, they didn't use ships on the Silk Road, and it brought better communications, etc. between countries.
Answer:
Deep ocean currents.
Explanation:
In cold regions, such as the North Atlantic Ocean, ocean water loses heat to the atmosphere and becomes cold and dense. When ocean water freezes, forming sea ice, salt is left behind causing surrounding seawater to become saltier and denser. Dense-cold-salty water sinks to the ocean bottom.
I think it is the first one
