动脉周围淋巴鞘是围绕（）动脉的淋巴组织，相当于淋巴结的（）区，为胸腺依赖区，含有大量的（）细胞。
参考答案：中央；副皮质；T
用所给动词的适当形式填空。
1. My brother started______ (learn) English when he was 5 years old.
2. Welcome to our class. I need______ ( ask) you some questions.
3.I will think about______ ( become) an engi-neer.
4.We decided______ (go) hiking this summer holiday.
5.—How long ______ you ______ (study) at the school? .
—For a year.
6.He______ (be) a college student for two years.
不属于凝血酶特点的是（）
A.是丝氨酸蛋白酶
B.能水解纤维蛋白原
C.激活血小板
D.激活抗凝系统的蛋白C
E.促进纤维蛋白（原）溶解活性
