Which 14th-century monastery, located about 70 kilometres north-east of Moscow in Sergiyev Posad, is the spiritual heart of Orthodox monasticism?

• A Optina Monastery
• B Valaam Monastery
• C Trinity Lavra of St. Sergius ✓
• D Solovetsky Monastery

Founded by Sergius of Radonezh around 1340, the Trinity Lavra (Троице-Сергиева лавра) is a UNESCO World Heritage site and the most important monastery, housing a seminary and the saint's relics.