You will be given a definition of a task first, then some input of the task.
Given a disfluent sentence, modify the sentence to it to its equivalent fluent form, preserving the meaning of the sentence.

How quickly is the sea level dropping or rather how long has the ongoing tectonic subsidence in the southern North Sea been happening for?
Output:
How long has the ongoing tectonic subsidence in the southern North Sea been happening for?