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【单选题】
下列命题中，正确的是 [ ]A.
关于x的方程x 2 =k，必有两个互为相反数的实数根
B.
关于x的方程（x﹣c） 2 =k，必有两个实数根
C.
关于x的方程ax 2 +bx=0（a≠0），必有一根是0
D.
关于x的方程x 2 =1﹣a 2 ，一定没有
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反馈参考答案：
举一反三
【单选题】He is generally considered _________the first computer. [ ]
A.
to have invented
B.
inventing
C.
to invent
D.
having invented
【单选题】He is generally considered _____ the first computer.
A.
to invent
B.
to have invented
C.
having invented
D.
inventing
【判断题】Zheng He was considered the first navigator to have traveled around the world in history.
A.
正确
B.
错误
【单选题】He is generally considered _____ the first computer. [ ]
A.
to invent
B.
inventing
C.
to have invented
D.
having invented
【判断题】Zheng He was considered the first navigator to have traveled around the world in history.
A.
正确
B.
错误
【单选题】First he considered the job of letters as a way of making a living, but as time went by, he developed a great passion for it.
A.
characters
B.
epistle
C.
writing
D.
mails
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