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【简答题】
已知关于x、y的方程2x 3a-2 -3y 2a+3b+5 =1是二元一次方程，求a 2 -2ab+b 2 的值．
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【单选题】The author implies that there is cause for concern if consumers with limited incomes buy organic goods instead of conventionally grown foods because
A.
organic foods can he more expensive but are often no better than conventionally grown foods
B.
many organic foods are actually less nutritious than similar conventionally grown foods
C.
conventionally grown foods are more readily available than organic foods
D.
too many farmers will stop using conventional methods to grow food crops
【单选题】The author implies that there is cause for concern if consumers with limited incomes buy organic foods instead of conventionally grown foods because ______.
A.
organic foods can be more expensive but are often no better than conventionally grown foods
B.
many organic foods are actually less nutritious than similar conventionally grown foods
C.
conventionally grown foods are more readily available than organic foods
D.
too many farmers will stop using conventional methods to grow food crops
【单选题】It is said that our body _______ 206 bones; if one of _____ is broken, it will cause inconvenience of some kind. [ ]
A.
makes up of; them
B.
is made up of; them
C.
is made up of; which
D.
makes up; which
【单选题】直接酸碱滴定法测定阿司匹林原料含量时的依据(原理)为（ ）。
A.
阿司匹林酯键水解，消耗氢氧化钠
B.
阿司匹林酯键水解，消耗盐酸
C.
羧基的酸性，可和氢氧化钠定量地发生中和反应
D.
水解后产生的醋酸和水杨酸消耗氢氧化钠
E.
阿司匹林分子的极性
【单选题】直接酸碱滴定法测定阿司匹林原料含量时的依据为( )
A.
阿司匹林酯键水解,消耗氢氧化钠
B.
阿司匹林酯键水解,消耗盐酸
C.
羧基的酸性,可和氢氧化钠定量地发生中和反应
D.
水解后产生的醋酸和水杨酸消耗氢氧化钠
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