短时间的一连串最大刺激作用于肌肉，若相继两次刺激间的时距小于绝对不应期时，后一次刺激

The film is very moving. I _____ it twice already.    [ ]

A. will see

B. see    

C. saw

D. have seen

金属在生产生活中应用广泛。

（1）下列厨房用品所使用的主要材料，属于金属材料的是________(填字母序号)。

A．不锈钢高压锅           B．陶瓷罐            C．铜火锅

（2）人类从自然界中提取金属。工业上用一氧化碳和赤铁矿（主要成分是氧化铁）冶炼铁的化学方程式为________；我国是世界上最早采用湿法冶金提取铜的国家，写出铁与硫酸铜溶液反应制取铜的化学方程式________。

（3）将一定量铁粉加入到AgNO₃、Cu(NO₃)₂、Zn(NO₃)₂的混合溶液中，充分反应后过滤，向滤渣中加入稀盐酸没有明显现象，则滤渣和滤液中溶质的组成可能为_________(填字母序号)。

十字头式柴油机活塞结构特点不正确的是（）。

A．新型活塞采用4道环

B．活塞环设在头部，承磨环设在裙部

C．环带应尽量靠近燃烧室

D．活塞裙部外径大于活塞头部外径

下列物质中最适合作为添加剂载体的是（）

A.磷酸二氢钙

B.苜蓿草粉

C.脱脂米糠

D.经过浸提油后的大豆粕

A conventional teacher’s licensee usually requires a university degree in education plus an unpaid term of practice teaching. This has never made much sense. It excludes bright students who take degrees in other subjects, and might teach those subjects; it is costly and time-consuming for career-switchers, who must wait a year or more before they can enter a classroom; it is so rigid that private-school teachers or university professors with years of experience have to jump through hoops before they can start teaching in a state school. And there is virtually no evidence that it creates better teachers. For all that, it is ply backed by schools of education, which have a monopoly of teacher-training, and by teachers’ unions, whose members make more money when it is artificially hard for others to get into the profession.

Now, some 45 states and the Districts of Columbia offer an "alternative route" to a teacher’s licensee, up from only a handful in the 1980s. Alternative certification (AC) generally allows individuals with a university degree to begin teaching immediately after passing an entrance examination. These recruits, watched over by a mentor teach the subject they studied at university, and take education courses at a sponsoring university while drawing their salaries.

The traditional sort of American teacher is likely to be young, white and female. Alternative certification attracts more men and more non-whites. In Texas, for instance, roughly 90% of public-school teachers are white, but 40% of those who have joined through alternative certification are non-whites. The AC route also draws teachers willing to go where they are most needed. A survey of Troops to Teachers, a program that turns exsoldiers into public-school teachers (" Proud to serve again"), found that 39% of those taking part are willing to teach in inner-city schools, and 68% in rural areas.

Are they good teachers Officialdom is reluctant to release the details which might answer that question for certain. But anecdotal evidence suggests they do well. In New Jersey, which has been running this sort of program since 1984, rich districts, which can afford to be choosy, consistently hire more AC teachers than poor districts do. In Houston, Texas, where the Teach of America program (TFA) puts recent university graduates into poor communities as teachers, the most effective teachers are generally the TFA ones. " School principals are our biggest fans," Wendy Kopp, TFA’s president, says proudly.

So why not scrap the cumbersome teacher-licensing laws Frederick Hess, a professor at the University of Virginia, has written a paper for the Progressive Policy Institute arguing that teacher-licensing ought to be stripped to the bare essentials. Prospective teachers should be required only to hold a college degree, pass a test of essential skills, and be checked to make sure they do not have a criminal background. Other training is important, argues Mr. Hess, but the market, not state legislators, should decide what that training looks like. This notion of "competitive certification" has drawn favorable attention from the Bush administration.

How does the author feel about the conventional teacher’s training（）

A. Ridiculous

B.Unjust

C. Complicated

D. Irrelevant