Today’’s lecture we’’ll center on the prehistoric people of Nevada Desert. Now most of these prehistoric desert people (36)______the countryside throughout the year. You might think that they’’re wandering aimlessly. Far from it, they actually followed the (37)______of carefully planned moves. Where they moved depended on where food was (38)______. Places where plants were ripening or fish were (39)______. Now often when these people moved, they carried all their (40)______on their backs. But if the journey was long, extra food and tools were sometimes stored in caves or (41)______rocks. One of these caves is now an exciting (42)______ site. Beyond its small opening is a huge underground (43)______. Even though the cave is very large. It was certainly too dark and dusty for the travelers to (44)____________. But it was a great place to (45)____________. And tremendous amounts of food supplies and artifacts have been found there.The food includes dried fish, seeds and nuts. The artifacts include stone spear points and (46)____________. The spear points are actually rather small. Here is a picture of some that were found. You can see their size in relation to the hands holding them.

我国院内感染最常见的菌属是（）

A.克雷伯菌属

B.肠杆菌属

C.哈夫尼亚菌属

D.沙雷菌属

E.枸橼酸菌属