This is considered the best move by theory, stopping the dangerous advance of the kingside pawns.
1. e2e4  1... c7c6  2. d2d4  2... d7d5  3. e4e5  3... c8f5  4. h2h4 This is one of the most interesting and popular options in the Advance Variation of the Caro-Kann. Black really needs to know what to do here.