A:In an hour.
B:For an hour.
C:One hour ago.
下列有关细菌及其生命活动的描述,正确的是( )
①以亲代DNA为模板合成子代DNA ②纺锤丝牵引染色体移向细胞两极 ③细菌可以发生的变异只有基因突变 ④基因工程中细菌质粒、噬菌体均可作为载体.
The children had to repeat that story twice,________they?