论述说明表达式在公文中的运用。

菠菜不仅含有大量的β胡萝卜素，也是维生素B₆、叶酸、铁和钾的极佳来源，但是菠菜不能直接烹调，吃菠菜时宜先用废水烫软，捞出再炒，在烹调前用沸水烫菠菜的主要原因是：( )

A．清除生菠菜含有的红血球凝集素

B．改变生菠菜内龙葵素的化学成分

C．防止菠菜内的草酸成分阻碍人体对钙的吸收

D．清除菠菜种植过程中残留的农药

5000米+6000米=______千米 1米-2分米=______分米

1500千克-500千克=______吨700千克+300千克=______吨．

IFT5无刷三相伺服电动机包括定子、转子、一个检测电动机转子位置及（）的无刷反馈系统。

Most critical plot points in Harry Potter and the Sorcerer’s Stone came from J. K. Rowling’s imagination, but Flamel and his powerful pebble were legendary long before Harry went to Hogwarts. The 14th century alchemist created the philosoper’s stone (called "sorcerer’s" in U.S.editions of Potter ), with which he turned mercury to gold and gained eternal life. But Flamel’s tale—like his stone and his science—was no more real than a magic.

The philosopher’s stone was the key to alchemy, the medieval predecessor to chemistry that aimed to cure all illnesses, make the elixir of life, and transmute base metals into gold. The last made perfect sense at the time. The Aristotelian theory of elements stated that all things consisted of fire, air, water, and earth. So a little shift in one metal’s composition could create gold.

Flamel was renowned as an alchemical success. In 1382, after 25 years of studying an ancient book by "Abraham the Jew", he is said to have produced the philosopher’s stone. His texts, notably a deconstruction of the "Abraham" work, were standard reading for aspiring scientists like Isaac Newton.

Many alchemists believed Flamel faked his 1418 death and that of his wife. Rumored sightings in the 18^th century placed them at the Paris Opera. As late as 1816 there were reports of people searching Flamel’s former house for secrets of the stone.

Contemporary historians say, a Nicolas Flamel did live in Paris in the 1300s and endowed many churches and hospitals with his wealth. But he was no alchemist. "He got his money in pedestrian ways—his wife’s earlier marriages, real-estate speculation," says lawrence Principe, author of The Aspiring Adept. Anachronisms, style of language, and the lack of earlier copies indicate that none of "his" writings originated prior to the 1500s.

"This sort of thing happens in alchemy," says Bill Newman, author of alchemical history Gehennical Fire. When an alchemist couldn’t back up his ideas, he might publish them in the guise of a "lost" work. Flamel’s wealth made a good candidate for alchemical identity theft.

Flamel writings and sightings faded with alchemy’s prestige. And the closest anyone’s come to the philosopher’s stone is Rowling. In her hands, it has yielded not just gold but eternal (shelf) life as well.

According to the passage, that Flamel gained eternal life with the aid of his powerful pebble ().

A. came from J. K. Rowing’s imagination

B. was legendary long before Rowling wrote the book

C. turned out to be a magic in Potter

D. was believed by many alchemists

下列哪个IP地址是组播地址（）

A.11.1.1.1

B.223.20.0.8

C.224.0.0.1

D.240.1.1.1