It exists in a double stranded form where every strand is matched by its complement.

这种碱基配对存在于DNA双链中,每条单链都与其互补链,通过这个原则配对组合

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That only strands that have this exact complement can form double stranded DNA.

这表示只有两条链的碱基对,完全互补才能形成DNA双链

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