Complex sentence: In 1976/77 he studied at the Catholic University, Washington, DC to obtain the Master degree in philosophy, and after returning he taught at the Lux Mundi seminary, the only major seminary in Thailand.
Split into simpler sentences: In 1976/77 he studied at the The Catholic University of America in Washington, DC from which he obtained a masters degree in philosophy. He then taught philosophy at the Lux Mundi seminary, the only major seminary in Thailand.