Question: Not Alone, is Zhang Liyin's which number overall single, Zhang held a showcase to support the release of the single, which was held at the Century Theater in Beijing, EXO members Tao and Chen were guests, Exois a South Korean-Chinese boy group based in Seoul? 
Sentence (from "Exo (band)"): It sold over one million copies, making Exo the best-selling Korean artist in twelve years.
Relevant evidence: No