简述D/A转换器的工作过程。

与BOT融资方式相比，ABS融资方式的特点包括______。

A．操作难度大

B．融资成本低

C．原始权益人保持项目运营决策权

D．能够获得国外先进管理经验

E．投资者风险小

Americans’ (1) impulses keep generating surprises. Charitable giving plays an even larger role in the (2) . Demand for nonprofit services gets proportionately bigger as a locality’s (3) rises. The philanthropy of the wealthy may not hinge on tax (4) to the degree many believe. The US (5) the world in levels of charitable activity. Some experts see charity as a (6) trait of the US, more than (7) or business. But those forces may be (8) , as many nonprofits, from healthcare to classical music are selling (9) in a marketplace alongside for-profit (10) . Charity is no mere (11) activity. It pays off for society in ways that may (12) the rates of return on many traditional investments. Charity not only helps those on the (13) end but also strengthens the (14) of society at large. Moreover, it appears to make the givers themselves more (15) . The pattern that conservatives are better givers than (16) is less about politics than about charity-linked (17) most common to conservatives, religious commitment, marriage and children, and entrepreneurship. The main point is that more Americans, regardless of ideology, embrace giving as a tool for (18) . The urge to make a difference, and to take (19) in it, outweighs (20) considerations.

基于“学生—选课—课程”数据库中的三 个关系是：

S(S#,SNAME,SEX,AGE),SC(S#,C#,GRADE),C(C#,CNAME,TEACHER) 若要求查找‘李’姓学生的学生号和姓名，正确的SQL语句是______。

A．SELECTS#,SNAMEFROMSWHERE SNAME=’李%’

B．SELECTS#,SNAMEFROMSWHERE SNAMELIKE’李%’

C．SELECTS#,SNAMEFROMSWHERE SNAME=’%李%’

D．SELECTS#,SNAMEFROMSWHERE SNAMELIKE’%李%’

下列关于氧炔焰的说法哪种正确（）？

A、中性焰是完全圆形光滑的、碳化焰外层火焰微明亮、氧化焰中心锥短，顶端比较尖，且带有蓝白色

B、碳化焰是完全圆形圆滑的、氧化焰火焰明亮

C、中性焰火焰明亮、氧化焰是完全圆形光滑的

D、氧化焰的光滑包络面是蓝色的

论述预防排浆泵无法吸浆的措施。