单选题作为神经递质，下列哪一种物质仅存在于中枢神经系统

单选题对于声波骨传导的叙述，恰当的是

单选题如下哪种肿瘤常分泌激素

单选题The United States experienced some of the most extreme weather events in its history this spring, including deadly outbreaks of tornadoes, near-record flooding, drought and wildfires. Damages from these disasters have already passed $ 32 billion, and the hurricane season, which is just beginning, is projected to be above average, according to the National Oceanic and Atmospheric Administration. Government scientists said Wednesday that the frequency of extreme weather has increased over the past two decades, in part as a result of global warming caused by the accumulation of carbon dioxide in the atmosphere. But they were careful not to blame humans for this year's rash of deadly events, saying that in some ways weather patterns were returning to those seen at the beginning of the last century. "Looking at long-term patterns since 1980, indeed, extreme climatological and meteorological events have increased," said Thomas R. Karl, director of NOAA's National Climatic Data Center. "But in the early part of the 20th century, there was also a tendency for more extreme events followed by a quiet couple of decades. " Presenting a new NOAA report on 2011 extreme weather, Dr. Karl said that extremes of precipitation have increased as the planet warms and more water evaporates from the oceans. He also said models suggest that as carbon dioxide builds up in the atmosphere and heats the planet, droughts will increase in frequency and intensity. "But it is difficult and unlikely to discern a human fingerprint, if there is one, on the drought record of the United States," he said. Some other climate scientists were more categorical about the human contribution to extreme climate events. Kevin Trenberth, distinguished senior scientist at the National Center for Atmospheric Research, said that when the greenhouse effect caused by burning fossil fuels is added to the natural variability of climate, weather disasters can be expected to occur more frequently. "Global warming is contributing to an increased incidence of extreme weather because the environment in which all storms form has changed from human activities," Dr. Trenberth said in a telephone interview Wednesday. "Records are not just broken, they are smashed. It is as clear a warning as we are going to get about prospects for the future. " April was a particularly devastating month for tornadoes and rainfall, with 875 tornadoes reported during the month and heavy rain and snowmelt contributing to Mississippi River flooding later in the spring that surpassed the historic floods of 1927 and 1937. So far this year, there have been nearly 1,400 preliminary tornado reports nationwide; those reports will most likely be whittled down to about 900 confirmed tornadoes, the second-highest annual total recorded in modern times. The record is 1,011 confirmed tornadoes in 2008. The year also is on track to be one of the deadliest, with 536 fatalities so far from tornadoes, placing 2011 in sixth place in United States history and the deadliest since 1936.

单选题男，36岁，酗酒时间约8年余。近半年来经常出现恶心、呕吐、食欲不振。肝穿刺显示肝细胞广泛脂肪变性，肝细胞灶状坏死。肝细胞内可见大小不等的红染的半透明小体。这些透明小体为

单选题导致各种躯体感觉的强度取决于

单选题下列描述中，哪种属于完全再生?

单选题肾盂肾炎最常见的致病菌是（ ）

单选题关于肿瘤实质的描述，下列不正确的是（ ）

单选题A．内含子 B．外显子C．断裂基因 D．mRNA的剪接E．拼接体

单选题甲胎蛋白阳性的肿瘤是

单选题 滤过分数是指 （ ） A、肾小球滤过率／肾血浆流量 B、肾血浆流量／肾血流量 C、肾血流量／肾血浆流量 D、肾小球滤过率／肾血流量 E、肾血流量／心输出量

单选题最常见的卵巢生殖细胞肿瘤是

单选题血吸虫卵主要栓塞于

单选题A．门静脉栓塞B．肺动脉栓塞C．肠系膜动脉栓塞D．脑动脉栓塞

单选题玻璃样变性不见于

单选题类风湿关节炎较具特异性的自身抗体是

单选题生物节律的控制中心多位于

单选题对于炎症时血管通透性增加的描述，哪项是不恰当的

单选题毛玻璃样肝细胞是指