[单项选择]下列对直链淀粉的描述正确的是（）
A. β-1，4葡萄糖苷键连接的线性葡聚糖
B. 天然食物中含量丰富
C. 遇碘产生棕色反应
D. 难消化吸收
E. 使血糖升高的幅度较支链淀粉小

We know that many animals do not stay in one place. Birds, fish and other animals move from one place to another at a certain time. They move for different reasons: most of them move to find food more easily, but others move to get away from places that are too crowded.
When cold weather comes, many birds move to warmer places to find food. Some fishes give birth in warm water and move to cold water to feed. The most famous migration (迁移) is probably the migration of fish, which is called "salmon". This fish is born in fresh water but it travels many miles to salt water. There it spends its life. When it is old, it returns to its birthplace in fresh water. Then it gives birth and dies there. In northern Europe, there is a kind of mouse. They leave their mountain homes when they become too crowded. They move down to the low land. Sometimes they move all the way to the seaside, and many of them are killed when they fall into the sea.
Recently, scie
A. Animals move in order to find food more easily.
B. The migration of the fish called "salmon" is the most famous migration.
C. Living things move from one place to another because they like to travel.
D. Sometimes we know why and how living things move from one place to another, but sometimes we don’t.