I've seen a lot of 500+ word answers on here, and not I don't think that's a bad thing at all, but for most of the answers, the point isn't conveyed until halfway through the answer.

Simply put, *began* is an adverb that is describing *spending*, the verb itself.
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> Why?

Because *began* is an adverb and *spending* is a verb (an adverb describes a verb, if you didn't get implication already).

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Sources:

http://esl.fis.edu/grammar/rules/adadv.htm (*Adjective or adverb?*)

http://grammar.ccc.commnet.edu/grammar/adverbs.htm (*In-depth*)