$2-$Snapchat, one of the fastest$-$growing social networks, can be an extremely effective $-$ When Ariana Grande or Kylie Jenner use asponsored filter, marketers have the opportunity to reach over $150$ million users a day in a fun way that doesn't look like a sponsored advertisement. $($Fill in the blank$).$

a$)$ Marketing tool

b$)$ Non$-$profit organization

c$)$ Environmental groups

d$)$ Marketing mix

e$)$ Marketing process