为了防止森林火灾，在森林里不允许随地丢弃透明的饮料瓶，这是由于雨水进入饮料瓶后对

什么是高压加热器的上、下端差？上端差过大、下端差过小有什么危害？

克山病是一种原因未明的地方性心肌病，山东省两次克山病流行均发生在病区居民生活困难时期，此时居民饮食结构单一，营养缺乏。1978年以后，由于农村经济体制的改革，病区居民生活逐渐好转，营养结构趋向合理，克山病新发病人越来越少，达到基本控制标准。一些研究者据此推测，营养缺乏可能是克山病发病的重要因素。
如果以下各项为真，哪项不能质疑上述推论( )

A．1978前农村生活水平普遍较低，但克山病仅在个别地方出现
B．原来克山病病区的土壤、水质在几十年中发生了较大变化
C．一些生活水平高的地区，也出现过克山病病例
D．通过调整饮食结构，无法治愈克山病

法律实效是指（）

A、前提

B、结果

C、过程

D、条件

An official report, addressing concerns about the many implications of genetic testing, outlined policy guidelines and legislative recommendations intended to avoid involuntary and/or ineffective testing, and to protect confidentiality. The report identified urgent concerns, such as quality control measures (including federal oversight for testing laboratories) and better genetics training for medical practitioners. It recommended voluntary screening, urged couples in high-risk populations to consider carrier screening, and advised caution in using and interpreting pre-symptomatic or predictive tests, because certain information could easily be misused or misinterpreted.

About three in every 100 children are born with a severe disorder presumed to be genetic or partially genetic in origin. Genes, often in concert with environmental factors, are being linked to the causes of many common adult diseases such as heart disease, hypertension (high blood pressure), various cancers, Alzheimer’s disease, etc. Tests to determine predisposition to a variety of conditions are under study, and some are beginning to be applied.

The report recommended that all screening, including screening of newborns, be voluntary. Citing the results of two different voluntary newborn screening programs, the report said these programs can achieve compliance rates equal to or better than those of obligatory programs. State health departments could eventually require the offering of tests for diagnosing treatable conditions in newborns, however, careful pilot studies for conditions diagnosable at birth need to be done first.

Although the report asserted that it would prefer that all screening be voluntary, it did note that if a state requires newborn screening for a particular condition, the state should do so only if there is p evidence that a newborn would benefit from effective treatment at the earliest possible age. Newborn screening is the most common type of genetic screening today. More than four million newborns are tested annually so that effective treatment can be started in a few hundred infants.

Prenatal (preceding birth) testing can pose the most difficult issues. The ability to diagnose genetic disorders in the fetus(胎儿)far exceeds any ability to treat or cure them. Parents must be fully informed about risks and benefits of testing procedures, the nature and variability of the disorders they would disclose, and the options available if test results are positive.

Obtaining informed consent—a process that would include educating participants, not just processing documents—would enhance voluntary participation. When offered testing, parents should receive comprehensive counseling, which should be nondirective. Relevant medical advice, however, is recommended for treatable or preventable conditions.

Genetics also can predict whether certain diseases might develop later in life. For single-gene diseases, population screening should only be considered for treatable or preventable conditions of relatively high frequency. Children should be tested only for disorders for which effective treatments or preventive measures could be applied early in life.

The report aims to（）

A. offer a detailed description of genetic testing process

B. stress the need for caution in the use of newborn screening

C. interpret the significance of genetic testing to the public

D. state the chief points of the policy guidelines on genetic screening

焊接需用的各类（）必须齐全、完好。