A. time B. period C. years D. age
A. He is too short. B. He is too tall. C. He is unusual.
A. for B. as C. with D. by
A. requiring B. asking C. looking D. preparing
A. 原始干细胞 B. 全能干细胞 C. 多能干细胞 D. 专能干细胞
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