Which of these advances did Han scientists make? Select all that apply. (2 points)
A. created more accurate calendars
B. devised the base-20 number system
C. developed the concept of zero
D. invented the compass
Which of these advances did Han scientists make? Select all that apply. (2 points)
A. created more accurate calendars
B. devised the base-20 number system
C. developed the concept of zero
D. invented the compass