生命科学是以实验为基础的学科，下列有关实验说法不正确的是（ ）
A：利用澄清的石灰水可以验证植物呼吸作用能否产生二氧化碳
B：“绿叶在光下制造有机物实验”中，用酒精直接对叶片进行脱色处理
C：探究“烟草浸出液对水蚤心率的影响”实验，必须控制的变量是烟草浸出液的浓度
D：“馒头在人口腔中的变化”的实验，可证明唾液能消化淀粉
判断一种材料是否比另一种更坚硬，可以用____的方法。
It was Sunday today. Tom with her two good friends are going to see his uncle . There are lots of apples trees on his uncle farm. But he is too busy to pick the apples in them. So Jim went to help him every year. The farm is no far from here. The children are all going there on bike . They think it's good for their healthy.
读《钢铁是怎样炼成的》，1920年8月，他在战争中负伤，导致____。
制作临时装片时，必须让盖玻片的一边先接触水滴，再轻轻盖上，目的是（ ）
