In which of the following situations should an employee provide a new Form W$-4,$ Employee's Withholding Certificate, to their employer?

a$.$ Hunter does not anticipate any changes to his income next year, and his withholding closely matches his last year's tax liability.

b$.$ Mark and Samantha are getting married and having a baby this year.

c$.$ Natasha estimated her tax return will result in a $$50$ refund. She is happy she does not owe and she wants to keep as much money in her pocket as possible.

d$.$Vera has worked at the same job for five years and has had no change in income.