Is it possible to select levels in the original version of Super Mario Bros 1?
What about Super Mario Mario Bros 2( the Japanese) ?
no.
You mean the Famicom and Famicom Disk System versions? Not directly, no. You can use Gamegenie or some other cheat device to do it, but there is no level selection in either game. There are level selects in Super Mario All Stars for SNES once you complete the games. SMB1 only allows you to select from the eight worlds while SMB2J allows you to select any stage.
There are also level selects for both titles in Super Mario Bros. DX for Gameboy Color.