What caused the battle of antietam to be the single bloodiest day in american history? a. confederate troops unexpectedly used guerilla tactics b. confederate troops outnumbered union troops 2 to 1 c. troops marched forward in close formation against newer, more accurate weapons

c. troops marched forward in close formation against newer, more accurate weapons

when in doubt choose c

it's what my teacher told my class when we were going into psats

offline recommendation systems option b

because recommendation systems produce a list of two ways

1. through collaborative filtering

or

2. through content-based filtering