题目

 I know he hasn't finished the work, but_______, he's done his best.                          A. above all          B. after all                 C. In all            D. At all 答案：B除去Na2CO3固体中少量NaHCO3的最佳方法是A．加入适量盐酸B．加热C．加入NaOH溶液D．配成溶液后通入CO2