问题 选择题

相同材质的铁在下列情形下最不易被腐蚀的是(  )

A.

B.

C.

D.

答案

A、铁做负极、铜做正极,食醋为电解质溶液,形成原电池,铁发生电化学腐蚀,故A不选;

B、铁做负极、合金中的碳等材料做正极,食盐水为电解质溶液,形成原电池,铁发生电化学腐蚀,故B不选;

C、铁被均匀的铜镀层保护,不易被腐蚀,故C正确;

D、铁做负极、铜做正极,酸雨为电解质溶液,形成原电池,铁发生电化学腐蚀,故D不选.

故选C.

单项选择题

So long as teachers fail to distinguish(differ) between teaching and learning, they will continue to undertake to do for children that which only children can do for themselves. Teaching children to read is not passing reading on to them. It is certainly not endless hours spent in activities about reading. Douglas insists that "reading cannot be taught directly and schools should stop trying to do the impossible".

Teaching and learning are two entirely different processes. They differ in kind and function. The function of teaching is to create the conditions and the climate that will make it possible for children to plan cleverly the most efficient system for teaching themselves to read. Teaching is also a public activity. It can be seen and observed.

Learning to read involves all that each individual does to understand the world of printed language. Almost all of it is private, for learning is an occupation of the mind, and that process is not open to public scrutiny.

If teacher and learner roles are not interchangeable, what then can be done through teaching that will aid the child in the long search for knowledge Smith has one principle rule for all teaching instructions. "Make learning to read easy, which means making reading a meaningful, enjoyable and frequent experience for children. "

When the roles of teacher and learner are seen for what they are, and when both teacher and learner fulfill them properly, then much of the pressure and feeling of failure for both is got rid of. Learning to read is made easier when teachers create an environment where children are given the chance to solve the problem of learning to read by learning.

The main idea of the passage is that ().

A. reading is more complicated than believable

B. reading ability is something gained rather than taught

C. teachers should encourage students to read as widely as possible

D. teachers should do as little as possible in helping students learn to read

单项选择题