Complex sentence: He studied Physics at the University of Athens and he graduated in 1971, continuing his studies at the University of Sussex in England, where he obtained his Ph.D. in 1973 in High Energy Physics.
Split into simpler sentences: He studied Physics at the University of Athens, graduating in 1971. He continued his studies at the University of Sussex in England, where he obtained his Ph.D. in 1973 in High Energy Physics.