You will be given a definition of a task first, then an example. Follow the example to solve a new instance of the task.
Answer the question from the given passage. Your answer should be directly extracted from the passage, and it should be a single entity, name, or number, not a sentence.

Passage: Martin Luther married Katharina von Bora, one of 12 nuns he had helped escape from the Nimbschen Cistercian convent in April 1523, when he arranged for them to be smuggled out in herring barrels. Suddenly, and while I was occupied with far different thoughts, he wrote to Wenceslaus Link, “the Lord has plunged me into marriage. At the time of their marriage, Katharina was 26 years old and Luther was 41 years old. Question: In a letter who did Luther credit for his union with Katharina?
Solution: the Lord
Why? The paragraph clearly states that, Luther has credited the Lord for his union with Katharina, hence the Lord is correct answer.

New input: Passage: As northwest Europe slowly began to warm up from 22,000 years ago onward, frozen subsoil and expanded alpine glaciers began to thaw and fall-winter snow covers melted in spring. Much of the discharge was routed to the Rhine and its downstream extension. Rapid warming and changes of vegetation, to open forest, began about 13,000 BP. By 9000 BP, Europe was fully forested. With globally shrinking ice-cover, ocean water levels rose and the English Channel and North Sea re-inundated. Meltwater, adding to the ocean and land subsidence, drowned the former coasts of Europe transgressionally. Question: What did frozen subsoil and expanded alpine glaciers begin to do?
Solution:
thaw