二次接线中的信号系统分为几种信号？各指什么？

设非空集合A，B满足A⊆B，则（　　）

A．∃x₀∈A，使得x₀∉B

B．∀x∈A，有x∈B

C．∃x₀∈B，使得x₀∉A

D．∀x∈B，有x∈A

Last August, Joe and Mary Mahoney began looking at colleges for their 17-year-old daughter, Maureen. With a checklist of criteria (衡量标准，尺度) in hand, the Dallas family looked around the country visiting half a dozen schools. They looked for a university that offered the teenager’s intended major (主修科目), one located near a large city, and a campus (大学校园) where their daughter would be safe.

“The safety issue (问题) is a big one,” says Joe Mahoney, who quickly discovered he wasn’t alone in his worries. On campus tours other parents voiced similar concerns (担心), and the same question was always  asked: What about crime? But when college officials al ways gave the same answer---“That’s not a problem here.” ---Mahoney began to feel uneasy.

“No crime whatsoever?” comments (评论) Mahoney today. “I just don’t buy it.” Nor should he: In 1999 the U.S . Department of Education had reports of nearly 400,000 serious crimes on or around our campuses. “Parents need to understand that times have changed since they went to college,” says David Nichols, author of Creating a Safe Campus. “Campus crime mirrors the rest of the nation.”

But getting accurate information isn’t easy. Colleges must report crime statistics (统计数字)  by law, but some hold back for fear of bad publicity (名声), leaving the honest ones looking dangerous. “The truth may not always be serious,” warns S. Daniel Carter of Security on Campus, Inc., the nation’s leading campus safety watchdog (监视) group.

To help concerned parents, Carter promised to visit campuses and talk to experts around the country to find out major crime issues and effective solutions.

小题1:The Mahoneys visited quite a few colleges last August_________.

A．to express the opinions of many parents

B．to choose a right one for their daughter

C．to check the cost of college education

D．to find a right one near a large city小题2:It is often difficult to get correct information on campus crime because some colleges_________.

A．receive too many visitors

B．mirror the rest of the nation

C．hide the truth of campus crime

D．have too many watchdog groups小题3:The underlined word “buy” in the third paragraph means “_________”.

A．mind

B．take

C．believe

D．expect小题4:What is the text mainly about?

A．Exact campus crime statistics.

B．Crimes on or around campuses.

C．Effective solutions to campus crime.

D．Concerns about kids’ campus safety.

风湿性心瓣膜病并发感染性心内膜炎时支持感染性内心膜炎诊断的是（）

A.体温38.5℃

B.胸痛并有胸膜摩擦音

C.超声心动图显示有赘生物

D.白细胞增高

E.心电图ST-T改变

用W_c=0.45%碳钢制造活动扳手，如发生硬度不足，试分析其原因。

临床医学研究中的保密原则（）。

A.欺骗、威胁、利诱进行医学临床实验违反了道德和法律

B.负担和受益要公正分配

C.受试者与研究者之间应保密

D.死亡家属有权获得赔偿

E.需获得伦理专家委员会（或主管部门）的批准