题目

Is human blood all the same? “Yes，” you may say．“It's all red．” Well，it's not as simple as you might think． Blood is made up of different parts，such as red blood cells，white blood cells，and platelets（血小板）． Two chemical molecules（分子）on the red blood cells make people's blood different．Scientists mark one molecule A and the other molecule B. According to which and how many molecules are on the red cell, scientists divide blood into four types: A, B, AB and O. Your blood type will stay the same your whole life. Scientists have been wondering if there 根据下面句子的意思写出相应的成语。 形容意志坚强，一点也不动摇。（　　）