Look at the timeline of some events in Dmitri Mendeleev’s life. Use the Past Perfect or the Past Simple to make sentences.

1. Before Mendeleev entered the Main Pedagogical Institute, he had lived in Tobolsk. 2. By the time he started his teaching career in Simferopol, he had received a strong education in science. 3. After he had received a master’s degree in chemistry, he joined the International Chemistry Congress in Germany. 4. Before he became a professor at the University of St. Petersburg, he had met many of Europe’s leading chemists. 5. By the time he discovered the periodic law, he had been working on the periodic table for many years.