input: Write a python function to convert a DNA sequence to its corresponding RNA sequence.
  assert convert_to_rna("ATCG") == "UAGC"
  assert convert_to_rna("GATTACA") == "CUAAUGU"
  assert convert_to_rna("CGT") == "GCA"
output: def convert_to_rna(dna_sequence):
      return dna_sequence.replace('A', 'U').replace('T', 'A').replace('C', 'X').replace('G', 'C').replace('X', 'G')