Black—box and white — box testing method are often used in software testing phase, in which, the white—box is mainly used to test software's( ).

A．reasonableness of structure

B．correctness of a program

C．external function of a program

D．internal logic of a program

如图为某核苷酸长链的示意图，下列相关叙述中，错误的是（）

A.图中所示为脱氧核苷酸长链

B.2为脱氧核糖

C.4为胞嘧啶脱氧核苷酸

D.5只能在细胞核中找到