Which sentence has a pronoun-antecedent disagreement error?

a. Each journalist has to decide what beat they want to cover.

b. It was so crowded that one of the girls lost her doll.

c. Every student should hand in his or her assignment.

d. Every boy scout has to sell his own cookies.

I believe that D. has an error. I think it should say "Every boy scout has to sell their own cookies." Rather than "Every boy scout has to sell his own cookies." This is because simply the fact that a "boy scout" would of course be a "him" or "his", and saying "his" makes the sentence sound weird.