Complex sentence: He resigned from the embassy to enroll in a program of chemistry and biology at in Montargis, a suburb south of Paris, and remained there for three years, then went on for further study at the Sorbonne University and the Pasteur Institute.
Split into simpler sentences: He resigned from the embassy to enroll in a program of chemistry and biology at in Montargis, a suburb south of Paris, and remained there for three years. He then went to Paris for further study at the Sorbonne University and the Pasteur Institute.