下列哪种是硫脲类抗甲状腺药可引起的严重不良反应（） A.黏液性水肿 B.心动过缓 C

恶性淋巴瘤患者开始治疗前应接受的手术称为（）

A.根治性手术

B.姑息性手术

C.预防性手术

D.诊断性手术

E.重建或康复手术

下面是分离硝酸钠和硝酸钙混合液的示意图：

回答下列问题：

（1）加入的盐是______，

（2）写出①、②所起反应的化学方程式．

______，______．

（3）滤液中加入适量HNO₃的原因______；

（4）在溶液蒸发获得晶体时，防止晶体损失的操作是______．

从地球向月球发射电磁波，经过2.56s收到它的反射波，月球、地球之间的距离是______km．

中国工程咨询协会和地方工程咨询协会按分级管理、( )方式进行执业检查。

A．责任到人

B．逐级上报

C．随机抽查

D．定期普查

E．定点调查

The most popular organic gem is the pearl. A pearl is the response of a marine mollusk to the presence of an irritating impurity accidentally introduced into its body; a cultured pearl is the result of the intentional insertion of a mother-of-pearl bead into a live mollusk. Whether introduced accidentally or intentionally, the pearl-making process is the same: the mollusk coats the irritant with a substance called nacre. Nacre is composed chiefly of calcium carbonate. Because very few natural pearls are now on the market, most pearls used in fine jewelry are cultured. These include "Biwa" pearls and most other freshwater pearls. Cultured pearls are not easily distinguished from natural pearls except by an expert.

What is the chief component of nacre

A．Sand.

B．Bead.

C．Calcium carbonate.

D．Biwa.