Sentence:  Through 1911 and 1912 , as the Cubist facet-plane 's tendency to adhere to the literal surface became harder and harder to deny , the <WSD>task</WSD> of keeping the surface at arm's length fell all the more to eye-undeceiving contrivances . 
Meaning of the word marked with <WSD> tags:  a specific piece of work required to be done as a duty or for a specific fee