Which of the following did Emma Witkowski (in "Counter-Strike: Spectatorship") NOT argue was among the factors contributing to the rise of Counter-Strike as a popular Esport?
a. Lack of microtransactions in Counter-Strike.
b. Valve's intellectual property agreement permitting third-parties to monetize Counter-Strike game broadcasts.
c. Valve sponsoring prize pools for major Counter-Strike tournaments.
d. Growth of Twitch as a streaming venue for Esports.