Write a function that accepts a string as an argument and display the string backwards

c++, pleaaaaaase solve the equation

python Please Write a function that finds the number of occurrences of a specified character in a string using the following header: def count(str, c) ex: count("welcome", "e") returns 2.

The following functions are all intended to check whether a string representing a dna sequence contains any characters that are not 'a','c','g','t', 'A', 'C', 'G', or 'T'. At least some of these functions are wrong. Which ones are correct? A) def valid_dna1(dna):     for c in dna:         if c in 'acgtACGT':             return True         else:             return False B) def valid_dna3(dna):     for c in dna:         flag = c in 'acgtACGT'     return flag C)   def valid_dna4(dna):     for c in dna:         if not c in 'acgtACGT':             return False     return True -------------------------------------------------------------------------------------------------------------------------------------------------------- valid_dna1 only valid_dna4 only None of them. valid_dna1, and valid_dna4 only