电力物资采购跟催方法是什么？

若二次函数y=x²-2x-k的图象与x轴有且只有一个交点，则k的值为______．

In the following essay, each blank has four choices. Choose the most suitable one from the four choices and write down in the answer sheet.
Open Shortest Path First(OSPF) is a (66) routing algorithm that (67) work done on the OSI IS-IS intradomain routing protocol. This routing, as compared to distance-vector routing, requires (68) processing power. The Dijkstra algorithm is used to calculate (69) OSPF routing table updates only take place when necessary, (70) at regular intervals.

A．but rather

B．rather too

C．rather than

D．rather that

硬母线焊缝应呈（），不应有毛刺、凹凸不平等缺陷。

下表是为了认识酶作用的特性，以20%的H₂O₂溶液为反应底物的一组实验。本实验结果不支持下列哪项结论（）

A.酶的催化条件具有温和性

B.酶的催化效率具有高效性

C.酶的催化对象具有专一性

D.高温会导致酶的活性丧失