“Mothers should remember that a nutritious breakfast is more important for a child than it is for an adult.”

Which of the following would be a better way to phrase this statement without bias?
a.
“Mothers should remember that a nutritious breakfast is more important for her child than it is for an adult.”
b.
“Parents should remember that a nutritious breakfast is more important for his or her child than it is for an adult.”
c.
“Mothers should remember that a nutritious breakfast is more important for his or her child than it is for an adult.”
d.
“Parents should remember that a nutritious breakfast is more important for his child than it is for an adult.”