Which of the following statements is TRUE when a new, higher minimum number of deleterious mutations appears in all individuals in an asexual population?
a. Future offspring can be produced with a different number of deleterious mutations, because of crossing over.
b. Recombination can help remove the new mutation.
c. Muller's ratchet hasn't turned yet.
d. Muller's ratchet cannot turn back (i.e., there is no reversing a deleterious mutation).