You are given an English sentence with a blank, and you need to predict the missing word. After completing, the whole sentence should be gramatically correct and non-ambiguous.

Let me give you an example: The kid on the street is ____ soccer
The answer to this example can be: playing
Here is why: This is the original sentence 'The kid on the street is playing soccer' So, we have correctly predicted the missing word to be 'soccer'

OK. solve this:
and although he found it rather difficult for his slower intelligence to keep ____ with her brisk mental processes
Answer:
up