Why didn’t people begin to use unmanned vehicles in undersea exploration until r

游客2023-10-06  21

问题 Why didn’t people begin to use unmanned vehicles in undersea exploration until recently?
It is because of the ______.
[br] Why is ocean exploration not so expensive as space travel?
Because ______ for submersibles to get away from the Earth’s gravity.

选项

答案 there’s no need

解析
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