Pushing c4-c5 in these positions is always a difficult choice, since White loses central control.
1. d2d4  1... d7d5  2. g1f3  2... c7c6  3. c1f4 The London System is always present, especially in blitz matches. 3... d8b6  4. d1c1  4... c8g4  5. e2e3  5... g8f6  6. c2c4 A new position on the sixth move already. 6... b8d7  7. b1c3  7... e7e6 