I don't get this, can someone help me

Their economies is based on sea ports, since most of cities are along the sea or are in rivers that connect to the ocean.

Explanation:

on this day in 1833, president andrew jackson announces that the government will no longer use the second bank of the united states, the country's national bank. a national bank had first been created by george washington and alexander hamilton in 1791 to serve as a central repository for federal fund

offline recommendation systems option b

because recommendation systems produce a list of two ways

1. through collaborative filtering

or

2. through content-based filtering