You will be given a definition of a task first, then some input of the task.
In this task, given a sentence in the English language, your task is to convert it into English Tokens.

He also warned that up to 250 million people in Africa could face what he called "increased water stress because of climate change."
Output:
He also warned that up to 250 million people in Africa could face what he called '' increased water stress because of climate change . ''