已知a是实数，则下列函数中，定义域和值域都有可能是R的是[ ]

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问题选择题

A．f(x)=x²+a

B．f(x)=ax²+1

C．f(x)=ax²+x+1

D．f(x)=x²+ax+1

答案

答案：C

填空题

根据汉语意思，写出单词。

1. How many ________ (糖) do you want in your coffee?

2. Could I have the ________ (食谱), please?

3. The coffee in his hand is a ________ (典型的) Italian cafe.

4. I have an ________ (疼痛) in my stomach.

5. It's a difficult task to ________ (教育) children.

填空题

金属指示剂会因为溶液中金属离子（）的变化而变色。