kung meron pre-requisite yung subject na yan , yung susunod nyan ay hndi mo po yata pwede ma-enrol, kailangan ay ipasa muna yan, bago yung ka-pre-requisite nyan.. example: Physics 1 , Physics 2, hndi ka muna makakapag physics 2 kapag hndi naipasa yung physics 1 (y)