题目

阅读下面短文，从短文后各题所给的四个选项（A、B、C和D）中， 选出可以填入空白处的最佳选项，并在答题卡上将该项涂黑。Todaywas a special day for me. What a privilege it was to have this opportunity tospread a little love and kindness! Ihad doctor's 1 ina town that's about 45 minutes from where I live. After both my appointmentswere 2, I left the building. I was about to 3 on my bicycle when I noticed an elderly womanstanding at the gate anxiously. I 4 myself and asked if she was waiting forsomeone or she needed 5.As it 6, she was having trouble 下列属于PCR技术的条件的是 ①单链的脱氧核苷酸序列引物②目的基因所在的DNA片段  ③脱氧核苷酸 ④核糖核苷酸⑤DNA连接酶⑥DNA聚合酶    ⑦限制性内切酶 A．①②③⑤ B．①②③⑥ C．①②③⑤⑦ D．①③④⑤⑦