为什么给汽封时必须先盘车？

我国高血压病最常见的死亡原因是（）。

A.尿毒症

B.合并冠心病

C.高血压危象

D.心力衰竭

E.脑血管意外

下列毒物经呼吸道吸入将会导致严重中毒的是 （）

A.浓硫酸

B.汞蒸气

C.浓氨水

D.砷

E.苯酚

某同学用粗细均匀的同一种导线制成“9”字形线框，放在有理想边界的匀强磁场旁，磁感应强度为B，如图所示，已知磁场的宽度为2d，ab=bc=cd=da=ce=ef=d，导线框从紧靠磁场的左边界以速度v向x轴的正方向匀速运动，设U₀=Bdv。在下图中最能体现be两点间的电压随坐标x变化关系的图象是

A、

B、

C、

D、

NOSA系统以风险管理为基础，强调人性化管理和持续改进的理念，目标是实现安全、健康、环保的综合风险管理。

The questions in this group are based on the content of a passage. After reading the passage, choose the best answer to each question. Answer all questions following the passage on the basis of what is stated or implied in the passage.

If you ask a person on the street to name the top predator in the sea, most people would probably say the great white shark. But they would be wrong. A great white shark is a relentless eating machine, superbly designed for its role at the top of the food chain, but the fact is, when a great white shark meets a killer whale, the killer whale has lunch. Not bad for an animal that is neither a whale nor a killer.

The killer whale, known to scientists as orcinus orca, is one of the largest, fastest, and most intelligent predators in the world’s oceans. The orca is not technically a whale, but rather the largest member of the dolphin family. The name "orca" has become the preferred name for the animal, because the name "killer whale" perpetuates the myth that orcas are dangerous to humans; in fact, there has never been a recorded incident of an orca attacking a human in the wild. This is not to say, however, that orcas are not dangerous to other marine species. Orcas in the wild have been observed consuming an astonishing variety of marine species, including salmon, tuna, sharks, giant squid, penguins, sea lions, dolphins, and even other whales, which the orcas hold under water until they drown. It is thought that the English name "killer whale" came from a mistranslation of the Spanish name asesina de ballenas, or "whale killer."

Despite decades of study, many aspects of the creatures’ life cycle and habits remain mysteries. Biologists only recently determined that there are, broadly speaking, three separate types of killer whale: residents, transients, and off shores. The residents live in large pods of up to 40 animals and primarily eat fish; these axe the most social of the killer whale types, with each pod having distinctive songs and complex social interactions. Transients are much quieter animals who roam large distances in groups of two to six while hunting marine mammals such as sea lions and dolphins. It is the transients who earned the orca the reputation of being whale killers. The third type of orca is the offshore variety, which rarely ventures toward coasts. These poorly understood animals travel in large groups, are somewhat smaller than their coastal cousins, and are thought to eat fish, sharks, and squid, but probably not other mammals.

Which of the following questions is most likely to represent one of the "mysteries" mentioned at the beginning of the third paragraph ？（）

A. Do all orcas maintain the same diet, or do some specialize in certain types of prey

B. Is the orca more closely related to whales or to dolphins

C. Do different orca pods exhibit any form of organization in their whale songs

D. Do orcas view swimming humans as a desirable source of food

E. What is the average lifespan of an orca of the offshore variety