今天全世界通用的纪年法是公元纪年，你知道这与传说中的哪一历史人物有关(    )       

若函数$f\left(x\right)=\frac{1}{\sqrt{2-x}}$的定义域为M，$g\left(x\right)=\sqrt{x+2}$的定义域为N，则$M\cap N=$( )

如图所示的是生物进化的大致历程（进化树）根据图回答下列问题：

下图表示人的个体发育过程。请据图回答：

（1）丁由甲细胞发育而来。则甲细胞的名称是____ 。

（2）由乙形成丙，细胞需要经过分裂、____ 和____ 的变化。

（3）甲到丁的过程，其同化作用____ （选填“大于”、“小于”或“等于”）异化作用。

（4）丁要完成一系列复杂的生命活动，需要在____ 和 ____ 的调节下实现。

    “USA? Britain? Which country is____(good) to study in?” We often hear such discussion. As China opens its door, it is a dream for many Chinese students to study abroad. They want to learn about the outside world.

    It's true that studying abroad can help students develop____(they). Their foreign language skills will____ (improve) and it may be easier to find jobs.

    But there are problems____ should be considered. Language is the first. Students must spend a lot of time____ (learn) another language.

    Students must also learn____ (live) without parents' care and deal with all kinds of things they didn't have to do before, like looking after themselves. There are ____ (report) about Chinese students abroad running into an ocean of difficulties____ giving up in the end. When they have to take care ____ themselves, it is hard for students to study well.

    Finally, studying abroad brings a heavy burden to the family. For most Chinese parents, the cost of studying abroad____ (be) very high. But is it worth it?