题目

单项选择 从每小题A、B、C、D中选出一个能填入句中空白处的最佳答案。 This is         3-D printer. And this is an artificial (人工的) ear. Can you believe that scientists printed this artificial ear by this 3-D printer? A. a                          B. an                            C. the                           D. / 答案：A

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