function DNAStrand(dna) {
  const arrayDNA = dna.split("");
  let complementaryDNA = "";

  arrayDNA.forEach((base) => {
    if (base === "A") complementaryDNA += "T";
    if (base === "T") complementaryDNA += "A";
    if (base === "C") complementaryDNA += "G";
    if (base === "G") complementaryDNA += "C";
  });

  return complementaryDNA;
}