深龋备洞可以不必达到的要求是
A.底平壁直
B.去尽腐质
C.保护牙髓
D.洞缘线圆钝
E.尽量保留健康牙体组织
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Tony and John are good friends. They like sports. Tony thinks basketball is interesting. He likes it very
much. He often plays basketball with his classmates. John doesn't like basketball. He likes playing soccer.
He thinks it's very exciting (令人兴奋的 ). Tony and John don't watch TV because it is boring.
根据短文内容,判断正(T)误( F)
( )1. Tony and John are good brothers.
( )2. Tony likes basketball.
( )3. John doesn't like soccer.
( )4. They like watching TV.
( )5. Tony thinks basketball is bonng.
乙烯在空气中的爆炸极限是()。
A.2.7%~32%
B.2.7%~36%
C.2.7%~37.2%
D.2.7%~72.7%
某患者服用一种药酒后,出现面部肌肉僵硬,反射亢进,角弓反张等症状。
该中药所含的有毒化学成分有()
A.马兜铃酸
B.三氧化二砷
C.马钱子碱
D.蟾酥碱
E.雷公藤苷
F.甘遂萜酯A
G.斑蝥素
H.士的宁
I.甘遂萜酯B
X、Y是除第一周期外的短周期元素,它们可以形成离子化合物XmYn,且离子均具有稀有气体原子的结构,若X的原子序数为a,则Y 的核电荷数不可能是:
A.a+8-m-n
B.a+16-m-n
C.a-m-n
D.a-8+m+n
我国在上海市投入运营的磁悬浮列车利用______磁极相互排斥的原理来实现悬浮,磁悬浮列车与一般火车相比较,具有______等优点.