Which of these advances did the han scientists make? select all that apply. a. created more accurate calendars b. devised the base-20 number system c. developed the concept of zero d. invented the compass

the answer is lower nubia. plz mark brainliest i am trying to improve rank.

offline recommendation systems option b

because recommendation systems produce a list of two ways

1. through collaborative filtering

or

2. through content-based filtering