如图,E,F是平行四边形ABCD的对角线AC上的点,CE=AF.求证:
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.
将质量为0.2kg的水加热,水的温度从20℃升高到40℃,水吸收的热量是多少?c水=4.2×103J/(kg·℃)
____