The alapin


1. e4 c5 2. c3 d5!?
3. d4 loses to 3. ...dxe4
You must defend the pawn or advance it, or play the daring exd5
3. e5?! 3. Nc6! simple and effective. 4. Nf3 g6 and black looks fine.
3. d3 is too passive. Black obtains an advantage with simple and normal play. Bg7, Nc6, b6 is a possibility.
3. exd5 is probably best. I still like black after 3. ...Qxd5!? when Nc3 is unplayable.
4. d4 e5!? a pawn that really isn't sacrificed. The Knight still can't come to c3, and Bf4 is unplayable now because of the e5 pawn.
5. dxe5 Nc6 the black pieces are better than the white pieces.
6. Nf3 Nxe5 not necessary, but not bad either.
7. Bf4!? Probably better than Nxe5 Qxe5+ Qe2/Be2, where Nf6, g6, etc leaves black with a slight edge (I believe).
7. ...Nxf3 8. Qxf3 Nf6 with a roughly equal position. Note that 8. ...Qxf3 is fine as well, messing the pawn structure.