Polish Teachers' Union
... that during World War II the Polish Teachers' Union was mostly active through the Secret Teaching Organization?
... that during <a href="./World_War_II" id="mwEAQ" rel="mw:WikiLink" title="World War II">World War II</a> the <b id="mwEAU"><a href="./Polish_Teachers'_Union" id="mwEAY" rel="mw:WikiLink" title="Polish Teachers' Union">Polish Teachers' Union</a></b> was mostly active through the <a href="./Secret_Teaching_Organization" id="mwEAc" rel="mw:WikiLink" title="Secret Teaching Organization">Secret Teaching Organization</a>?