As a rule,  Black prefers not to trade on e3 as this will open a valuable file for the first player.
1. e2e4  1... e7e5  2. g1f3  2... b8c6  3. f1c4  3... f8c5  4. d2d3  4... g8f6  5. a2a4  5... e8g8  6. a4a5  6... a7a6  7. e1g1  7... h7h6  8. c2c3  8... d7d6  9. h2h3  9... c5a7  10. c1e3 