Web Science/Part2: Emerging Web Properties/Simple statistical descriptive Models for the Web/Counting Words And Documents/quiz

{How many words are in the following sentence? It is really really difficult to count words.} - 6 - 7 + 8 - 9

{How many unique word tokens are in the following sentence? It is really really difficult to count words.} - 6 + 7 - 8 - 9

{which of the following command line tools can be used to count words?} - cat - ls + wc + tr