their vs. his/her and something else

[Season82]

ok, I am confused with these exercises, can someone help me? Thanks

The amount of time students spend researching a topic depends on his
familarity with the topic. (a?)
a. students spend researching a topic depends on his or her familiarity
b. students spend researching a topic depends on their familiarity

The school district newsletter informs all parents of beneficial programs for you and your children. (b?)
a. all parents of beneficial programs for your children,
b. each parent about beneficial programs for you and your children,
c. you of all beneficial programs for you and your children,
d. no change

[Jamie (K)]

In the first pair, (b) is correct, because "students" is plural, and the pronoun "their" has to agree with that word.

In the second one, all of the answers are ungrammatical. It should say, "The school district newsletter informs all parents of beneficial programs for them and their children."