What is the grid system in Bootstrap?

Question $6$ options:

$1)$

A system that divides your web page into $12$ equal columns that can be resized and rearranged according to different screen sizes

$2)$

A system that displays your web page as a grid of squares that can be filled with different colors and images

$3)$

A system that aligns your web page elements along horizontal and vertical lines that can be spaced and styled according to different preferences

$4)$

A system that creates a grid$-$like structure for your web page elements using tables and cells