物质的用途与其性质密切相关．

（1）医疗急救时需要氧气，是因为氧气能____ ；

（2）用墨汁书写或绘制的字画能够保存很长时间不变色的原因是____ ．

阅读短文，完成句子。
    Lychees grow in the south (南方) of China. They are small with red peel (果皮). Most people like to eat them, because they are sweet and full (充满的) of juice.  There is an old story about lychees. Yang Yuhuan loved lychees very much. Lychees have a lot of vitamin C. It is very important for people. Vitamin C can make children more healthy. So many parents often buy lychees for their children. Amy and her mum are in the fruit shop now. What fruit are they going to buy? Look! They are buying lychees
从文章中找到适当的单词或短语填空，完成句子。

下表是实验测得的四种植物分生组织的细胞周期，下列叙述正确的是(    )

5－溴尿嘧啶（Bu）是胸腺嘧啶的结构类似物，在含有Bu的培养基上培养大肠杆菌，得到少数突变型大肠杆菌。突变型大肠杆菌中的碱基数目不变，但（A+T）与（C十G）之比略小于原大肠杆菌，这表明Bu诱发基因突变的机制是（   ）

工人师傅要做4个棱长是1.5分米的正方体混凝土块做压力实验，至少需要混凝土____立方分米。