____

请回答下列问题（对应元素均用元素符号表示）：

    On March 14, maths and science lovers around the world celebrated a special day: Pi Day.

    Pi is____ to3. 14, but the number goes on endlessly. It is sometimes written in Greek,π. With the help of computers, mathematicians have been able to ____ pi out to over trillion (万亿) decimal places, but there is still no____ to the number. This makes pi puzzling, even for the most famous scientists and mathematicians.

    Pi Day is celebrated around the world on March 14, since how we write this date, 3/14,looks just like the number pi.

    For some people, the appeal (吸引力) of Pi Day goes far beyond maths and science. Pi shows up____popular culture. You can see it in movies, comics, music and more. "In modern movies, any time the filmmaker wants to evoke (产生) a sense of mystery, often the symbol pi is used, "says David Blatner, Jewish American writer of The Joy of Pi.

看图，选词填空。

A: ____ is the dog?

B: It's ____ the door.

已知镁可以在某种气体中燃烧，用化学方程式表达为：2Mg+X2MgO+C，则X的化学式为____ ；该反应属于四种基本反应类型中的____ 反应．标出氧化镁中镁元素的化合价____ ．