连铸坯的激冷层比模铸钢锭的激冷层（）
A.厚
B.薄
C.脆
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| Mr. Green works in an office in Chicago. 1 Saturday, he went to the office to do some work. When he got on the elevator, it stopped between the 2 . Mr. Green could not get out of the elevator. He started to 3 , but no one 4 him. Then Mr. Green remembered that it was a holiday in America. No one was going to come to work 5 Tuesday. There was 6 for him to do. He had to wait. With nothing to eat 7 drink, Mr. Green slept for most of the time. Early Tuesday morning, his 8 came to work and found the elevator was not working. When the elevator was 9 , Mr. Green came out. He was cold, weak, and tired. He had been in the elevator for about sixty-four 10 ! Now Mr. Green says, "I will only use elevators if they have a telephone in them."
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下列说法正确的是（ ）
A．医疗上常用75%（体积分数）的酒精作消毒剂
B．加碘食盐中的“碘”通常是指碘单质
C．体操运动员所用的防滑“镁粉”，其成分是金属镁
D．使用明矾可软化硬水
根据考古发现，人类历史上最早的城市出现在( )。
A．公元前5000年左右
B．公元前4000年左右
C．公元前3000年左右
D．公元前2000年左右
常发生晕厥的瓣膜病变是（）
A.肺动脉瓣狭窄
B.主动脉瓣狭窄
C.二尖瓣关闭不全
D.主动脉瓣关闭不全
E.三尖瓣狭窄
球童服务完毕之后要向巡场报告服务情况，填写任务完成表