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.①②③⑤B.①②③⑥C.①②③⑤⑦D.①③④⑤⑦ 答案:BI don’t really work here,I until the new secretary arrives.? A.just help out B.have just helped out? C.am just helping out D.will just help out?