领导的实质是一个（）。A、社会组织系统 B、行政组织系统 C、经济组织系统 D、干部组织系

如下图甲所示，质量为m=1kg的物体置于倾角为θ=37°固定斜面上，对物体施以平行于斜面向上的拉力F，t₁=1s时撤去拉力，物体运动的部分v-t图像如图乙。

试求：

t=4s时物体的速度v。

下列对形成龋齿的原因描述不精确的选项是().

A、乳牙牙釉质薄 

B、牙本质较松脆 

C、容易被腐蚀 

D、乳牙较小

下列叙述中，正确的是______。

A．高级程序设计语言的编译系统属于应用软件
B．高速缓冲存储器(Cache )一般用SRAM来实现
C．CPU可以直接存取硬盘中的数据
D．存储在ROM中的信息断电后会全部丢失

妊娠合并外科疾病时是否能施行麻醉和手术，哪项错误

A．必须考虑孕妇和胎儿的双安全性
B．区域阻滞相对优于全身麻醉
C．择期手术可在4个月以后施行
D．整个妊娠期间应避免施行所有择期手术
E．急症手术在麻醉时充分供氧，避免缺氧和低血压

Animal studies are under way, human trial protocols are taking shape and drug makers are on alert. All the international health community needs now is a human vaccine for the bird flu pandemic sweeping a cluster of Asian countries.

The race for a vaccine began after the first human case emerged in Hong Kong in 1997. Backed by the World Health Organization (WHO), three research teams in the US and UK are trying to create a seed virus for a new vaccine. Their task is formidable, but researchers remain optimistic." There are obstacles, but most of the obstacles have been treated sensibly," says Richard Webby, a virologist at St. Jude Children’s Research Hospital in Memphis, Tennessee.

The biggest challenge is likely to be the rapidly mutating virus. Candidate vaccines produced last year against the H5N1 virus are ineffective against this year’s strain. Scientists will have to constantly monitor the changes and try to tailor the vaccine as the virus mutates. They can’t wait to see which one comes next.

The urgency stems from fears that I-ISN1 will combine with a human flu virus, creating a pathogen(病原体) that could be transmitted from person to person. But if people have no immunity to the virus, the strain may not mutate as rapidly in people as it does in birds.

To quickly generate the vaccine, researchers are using reverse genetics, which allows them to skip the long process of searching through reassorted viruses for the correct genetic combination. Instead, scientists clone sequences for hemagglutinin(红血球凝聚素) and neuraminidase(神经氨酸苷酶), the two key proteins in the virus. The sequences are then combined with human influenza genes to create a customized reference strain.

Because products developed with reverse genetics have never been tested in humans, the candidate vaccines will first have to clear regulatory review. In anticipation, the US Food and Drug Administration (FDA) and the European Agency for the Evaluation of Medicinal Products (EMEA) are both preparing pandemic response plans. The EMEA has produced a fist-track licensing program, an industry task force and detailed guidance for potential applicants.

In Europe, a reassortant influenza virus -- but not the inactivated vaccine -- produced by reverse genetics would be considered a genetically modified organism, and manufacturers would need approval from their national or local safety authorities. The WHO has prepared a preliminary biosafety risk assessment of pilot-lot vaccine, which could help speed up the review.

A preliminary version of their protocol calls for several hundred subjects, beginning with a group of young adults and gradually expanding to include those most susceptible to the flu -- children and the elderly." If we had product," says Lambert," it would probably be a couple of months at the earliest before we have early data in healthy adults.

The vaccine generated by reverse genetics is required to review in that （）

A. it has p side effect to the elderly

B. it may turn ineffective in a short period

C. it is useless in preventing the virus

D. it hasn’t been tested in humans