急性肺栓塞抗凝治疗的常用药物有（）

A.普通肝素

B.抗血小板药物

C.尿激酶

D.链激酶

E.rt-PA

For（1） service, we need a virtual-circuit subnet. Let us see how that works. The idea behind virtual circuits is to avoid having to choose a new （2） for every packet sent. Instead,when a connection is established, a route from the （3）machine to the destination machine ischosen as part of the connection setup and stored in tables inside the（4）That route is used forall traffic flowing over the connection, exactly the same way that the telephone system works.When the connection is released, the virtual circuit is also terminated. With connection-orientedservice, each packet carries an （5）telling which virtual circuit it belongs to.

（3）是（）

A.source

B.route

C.destination

D.host