Why did christopher columbus travel around the world?

Which plan proposed to maintain open trade between china and western nations? open door policy national sovereignty missionary diplomacy salutary neglect

If you lived in greece in about 300b.c. you had a good chance of witnessing which of the following? select all that apply

Describe the technology advancements that lead to explorers being able to sail great distances. [[ps: doesn't explain where. i am only speculating it's in europe.