Question: Pentatonix, the five-member American a cappella group lost their vocalist Avi Kaplan in 2017 at the same time as their tribute to which group received over 250 million views?
Sentence (from "Pentatonix discography"): American a cappella group Pentatonix has released four studio albums, four extended plays (EPs), eight singles and twenty six music videos.
Relevant evidence: No