Sergio and Sally have a very diverse family. Which of the following children would not be a qualifying child for the purpose of claiming the child tax credit in 2023?

a) Their 5-year-old son who lives with them year-round.
b) Their 17-year-old daughter who is a full-time student and lives with them for more than half the year.
c) Their 19-year-old niece who lives with them for the entire year but provides over half of her own financial support.
d) Their 15-year-old adopted son with special needs who lives with them for the entire year and is fully dependent on them for support.