A:(﹣2,﹣1)
B:(﹣1,0)
C:(0,1)
D:(1,2)
如图是一个物体所受重力的示意图,其中正确的是( )
根据句子意思,用括号中所给词的正确形式填空,每空填一词。
Seven ____ (twelve) of the students have taken part in the tree-planting activity since Monday.
已知:2CH3CHO →NaOH CH2CH(OH)CH2CHO →△ CH2CH=CHCHO