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【单选题】
下面哪一个不是正确的标识符A.
$persons
B.
this
C.
_1234
D.
hello
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参考解析：
知识点：
皮皮学刷刷变学霸
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【简答题】已知矩阵A＝ (k≠0)的一个特征向量为α＝ ，A的逆矩阵A －1 对应的变换将点(3，1)变为点(1，1)．求实数a，k的值．
【单选题】If nothing is done to protect the environment, millions of spiders that are alive today will have become ________.
A.
deteriorated
B.
degenerated
C.
suppressed
D.
extinct
【单选题】If nothing is done to protect the environment, millions of spedes that are alive today will have become ________ .
A.
deteriorated
B.
degenerated
C.
suppressed
D.
extinct
【单选题】If nothing is done to protect the environment, millions of species that are alive today will have become _____.
A.
deteriorated
B.
degenerated
C.
suppressed
D.
extinct
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