1.Nf3 f6 2.e3 e6 3.Nd4

Black can try 3...c6, 3...f5, 3...Bb4 4.c3 f5 (if 4...Bxc3 then 5.Qh5+ g6 6.Qc5 d6 7.Qxc7) or 3...Nh6.

Black can't play 3...b5 or 3...a6 due to 4.Nf5.