每题2分，共10分 1、 Forms of Environmental Disease 46 . How the diseases are expressed depends on how the particular environmental agent enters the body, how it is metabolized(引起代谢)，and by what route it is excreted. The skin, ungs,liver,kidneys,and47 . Of particular concern is the capacity of many environmental agents to cause various cancers, birth defects or spontaneous affection (through fetal exposure), and mutations(突变)in germ cells, 48 . Environmental illnesses can be mild or severe and range from transient to chronic, depending on the doses of toxin(毒素)received. Some diseases occur abruptly at a toxic exposure, whereas the time of onset of other diseases varies after exposure. 49 . Those illnesses that occur directly after a distinct toxic exposure are usually easily identified as being environmentally or occupationally caused. If the exposure is not clear-cut or illness is delayed, however, the cause is difficult to identify, as clinical features alone are usually nonspecific. 50 . In such instances, epidemiological studies of exposed populations can help relate exposures to the illnesses they cause. A Environmentally induced cancers, for example, commonly involve latency (潜伏期)periods of 15 to 30 years or more B In addition, many different causes, environmental or otherwise, may produce identical illnesses C However, the reverse is true D nervous systems are commonly affected by different agents in different settings E the last?named raising possibilities of environmentally caused genetic diseases in later generations F Environmental diseases can affect any organ system of the body
