A:矛盾双方必然相互转化
B:量变到一定程度必然会引起质变
C:事物发展是内因与外因的统一
D:事物是在曲折中发展的
—I often go to school on ___ bike. But this morning I took a bus.
计算:cot45°+tan60°2sin60°-cos60°﹣cot30°