第21题: [单项选择]耳能感觉到的声音频率范围是( )。 A. 200~20000Hz B. 20~20000Hz C. 200~200000Hz D. 20~200000Hz 参考答案:B
第22题:[单选题] —These problems are too hard to . Will you give me some advice?—There are many ways, but the most important is to have a careful plan.( ) A. work out B. look out C. hand out D. put out 参考答案:A
第23题: [单项选择]机体内铁的排泄途径不包括() A. 由皮肤丢失 B. 呼吸道黏膜细胞脱落 C. 主动排铁 D. 泌尿系统黏膜细胞脱落 E. 胃肠道黏膜细胞脱落 参考答案:C