A very topical line, in part because of Wesley So's contribution to it.
1. d2d4  1... g8f6  2. c2c4  2... e7e6  3. b1c3  3... f8b4  4. e2e3  4... e8g8  5. f1d3  5... d7d5  6. c4d5  6... e6d5  7. a2a3  7... b4d6 