A:使用环形玻璃棒既可以搅拌又避免损坏温度计
B:测了酸后的温度计要用水清洗后再测碱的温度
C:向盛装酸的烧杯中加碱时要小心缓慢以免洒出
D:改变酸碱的用量,所求中和热数值不变
When the teacher got into the classroom, all the students stopped _______ at once.