A. to have left B. to be leaving C. to leave D. to have been left 参考答案:A 答案解析:[分析] 本题测试点为动词不定式的时态。动词不定式的完成体表示不定式的动作发生在谓语的动作之前，本句中leave这一动作应该在上周发生，所以动词不定式应该用完成体。例如：I was pleased t
第10题: [单项选择]关于探针的叙述不正确的是（）。 A. 探针长度一般是十几个碱基到几千个碱基不等 B. 要加以标记、带有示踪物，便于杂交后检测 C. 具有高度特异性，只与靶核酸序列杂交 D. 应是单链，若为双链用前需先行变性为单链 E. 作为探针的核苷酸序列要选取基因非编码序列 参考答案:E 答案解析:作为探针的核苷酸序列要选取基因编码序列，避免用内含子及其他非编码序列。
A. He had sent his brother abroad. B. He had cheated his brother out of his inheritance. C. He had given just a little share of the inheritance to his brother. D. He had gone abroad leaving his brother nothing. 参考答案:B 答案解析:[解析] 本题考查细节。参见第二段第四句话as executor of his father's will，he had been cheating his brother，who lived abr
第27题: [单项选择]下列试剂中，可以作为镉测定的基体改良剂是（）。 A. 氯化钠 B. 硫酸钠 C. 磷酸钠 D. 钼酸 E. 抗坏血酸 参考答案:C 答案解析:基体改良剂对于抑制基体干扰有一定作用。
