题干

当镁原子由1s22s22p63s2→1s22s22p63p2时,以下认识正确的是(  )

A:镁原子由基态转化成激发态,这一过程中吸收能量

B:镁原子由激发态转化成基态,这一过程中释放能量

C:转化后位于p能级上的两个电子处于同一轨道,且自旋方向相同

D:转化后镁原子与硅原子电子层结构相同,化学性质相似

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A

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    Currently offered by some famous universities, MOOCs are attractive to people who do not have the financial resources to meet the growing costs of university education, or who do not have formal qualifications. They also allow participants to study at their own pace.

    The potential for MOOCs to deliver education is obviously vast—they could be considered as a huge step forwards in widening participation. They also have the potential to provide a unique window on universities that offer popular and valuable courses, they may attract some participants to register for formal fee-paying programmes at the same or other universities and are likely to promote new ways of on-line education.

    However, it is still very early days for MOOCs. The quality of the education provision is highly variable, with many courses offering only recordings of lectures, and delivery is particularly difficult in some special fields that require practical classes, research projects or extensive library access. Besides, wider engagement with participants requires very considerable resource. Even limited feedback or examination becomes a major task if there are several thousand students in the class.

Considering the challenges, some people argue MOOCs will soon evaporate (蒸发). But they certainly provide good opportunity for widening higher education, are a means of raising awareness of universities to audiences of tens or hundreds of thousands, and are well worthy of serious consideration.