it would take the ocean about 4000years to dry up.能改成ocean take about 4000years to dry

it would take the ocean about 4000years to dry up.能改成ocean take about 4000years to dry
it would take the ocean about 4000years to dry up.能改成ocean take about 4000years to dry

it would take the ocean about 4000years to dry up.能改成ocean take about 4000years to dry
不能改成ocean take about 4000years to dry up
It takes sb some time to do sth 意思是：干某事花费某人多少时间（to do sth 是真正的主语,it是形式主语） （take的主语不能是人,只能是事）
你的句子中the ocean 相当于sb.

不能，应该是To dry up the ocean would take about 4000 years。 形式主语中真正的主语在最后，所以把to do 不定式提前就行了。

不能，后面的话要用被动语态、、而且to do sth 是真正的主语，take没加s