19 points ! @! @@! @ why was the open-border policy important for enabling china to prosper during the rule of the song dynasty? select all that apply. ( you need to pick 2) a. chinese farmers could produce two rice crops per year, selling one for cash. b. china could introduce and sell new kinds of tea throughout southeast asia. c. traders could sell many varieties of chinese spices in faraway markets. d. chinese merchants could import faster-growing rice from southeast asia.