Question: What is a significant mosque in Istanbul, made of two former Eastern Orthodox churches and a chapel,  Istanbul High School, or Zeyrek Mosque?
Sentence (from "Istanbul High School"): İstanbul High School, (Turkish: İstanbul Lisesi , German: Istanbuler Gymnasium ) also commonly known as İstanbul Erkek Lisesi, abbreviated İEL, is one of the oldest and internationally renowned high schools of Turkey.
Relevant evidence: Yes