女性，67岁，近1年来感头晕、乏力、记忆力减退、面色苍白；因急性阑尾炎手术治疗，术后

双受精现象只存在于 ① 门植物。

KAl（SO₄）_m常用作净水剂，如果K为+1价，Al为+3价，那么m值应为（　　）

A．1

B．2

C．3

D．4

课文填空

Did you know that tea, the most popular drink in the world (after water), was invented by __________? Although tea wasn’t brought to the Western world _________ 1610, this beverage was __________ over three thousand years before that. __________ to an ancient Chinese legend, the emperor Shen Nong discovered tea when he was _________ drinking water __________ an open fire. Some __________ from a nearby bush fell into the water and __________ there for some time. The emperor noticed that leaves in the water produced a pleasant __________. Later he decided to taste the hot mixture. It was quite delicious. And _________ this way, one of the world’s favorite drinks was invented.

某企业将一处房产转让给某国家机关办公使用，则本次房产转让行为无需缴纳契税。（）

煤炭在我国能源结构和国民经济中的地位举足轻重，是我国的（）能源，在一次能源消费结构中的比重占（）多。