____ to Anne's birthday party, Mr. Brown is now searching shop after shop for a nice present for her.

A．Having invited

B．Having been invited

C．Have been invited

D．Being invited

血浆中主要的天然抗凝物质有（）

A.肝素

B.纤维蛋白溶解酶

C.抗凝血酶III

D.柠檬酸钠

E.Ca2+