Not one rope, not a single cord, double......to make it stronger......

Yes, in DNA, the nitrogenous bases always pair in a specific way: adenine (A) with thymine (T), and guanine (G) with cytosine (C). This is known as complementary base pairing, where the two strands of the DNA double helix are held together by hydrogen bonds between these specific base pairs.
 

The pairing rules: 

• A always pairs with T: (and T always pairs with A).
• G always pairs with C: (and C always pairs with G).

Why this pairing is important:

• Structure:

  The A-T and G-C pairs form the "rungs" of the DNA ladder, with the sugar-phosphate backbones on the outside. 
• Stability:

  A-T pairs are held together by two hydrogen bonds, while G-C pairs are held together by three hydrogen bonds, making G-C pairs stronger.