题目

语法填空A young man, while【1】( travel) through a desert, came across a spring of clear water. The water was sweet. He filled his leather container so that he could bring some back to an elder【2】had been his teacher. After a four–day journey, the young man presented the water to the old man. His teacher took a deep drink, smiled warmly, and thanked his student very much【3】the sweet water. The young man went home with a happy heart.After the student 【4】(leave), the teacher let another student taste the water. He spit it out,【5】(say) it was awful. Obviously, it was no lo7．如图表示人体内特异性免疫的过程，图中A、B、C、D代表几种免疫细胞，据图回答下列问题：（1）图中A、D分别表示B细胞、效应T细胞．（2）免疫活性物质包括淋巴因子、抗体、溶菌酶等．（3）C在发挥免疫作用时将产生抗体，其化学本质是蛋白质（或免疫球蛋白）．