字符比较大小实际是比较它们的ASCII码值，下列比较中正确的是( )。A．“A”比

生态系统的能量流动和物质循环都是通过______和______实现的，这两个过程密切相关、不可分割．

下列说法正确的是 ( )

A．同周期的IA族元素的金属性比IIA族的元素金属性强

B．第三周期元素的阴离子半径从左到右逐渐增大

C．VIA族的气态氢化物一定比VA族的稳定性强

D．原子晶体的熔点一定比离子晶体的高

局限工期鼻腔NK/T细胞淋巴瘤放疗野不包括（）。

A.受侵同侧鼻腔

B.受侵对侧鼻腔

C.同侧上颌窦

D.前组筛窦

E.颈部淋巴引流区

牙髓炎症的主要感染途径（）

A．深龋

B．外伤

C．发育异常

D．牙周袋

E．楔状缺损

Scientists around the world are racing to learn how to rapidly diagnose, treat and stop the spread of a new, deadly disease. SARS — Severe Acute Respiratory Syndrome — was (1) for the first time in February 2003 in Hanoi, (2) since then has infected more than 1,600 people in 15 countries, killing 63. At this (3) , there are more questions than answers surrounding the disease.

Symptoms start (4) a fever over 100.4 degrees F, chills, headache or body (5) . Within a week, the patient has a dry cough, which might (6) to shortness of breath. In 10% to 200% of cases, patients require (7) ventilation to breathe. About 3.5% die from the disease. Symptoms (8) begin in two to seven days, but some reports suggest it (9) take as long as 10 days. Scientists are close to (10) a lab test to diagnose SARS. In the meantime, it is diagnosed by its symptoms. There is no evidence (11) antibiotics or anti-viral medicines help, (12) doctors can offer only supportive care. Patients with SARS are kept in isolation to reduce the risk of (13) . Scientists aren’t sure yet, but some researchers think it’s a (14) discovered coronavirus, the family of viruses that cause some common colds.

Most cases appear to have been passed (15) droplets expelled when infected patients cough or sneeze. Family members of infected people and medical workers who care for them have been most likely to (16) the illness. But recent developments in Hong Kong suggest that the (17) might spread through air, or that the virus might (18) for two to three hours on doorknobs or other (19) Health experts say it is (20) , though, that sharing an elevator briefly with an infected person would be enough to pass the virus.

17（）

A.ailment

B.ill-health

C.disease

D.infection