Which of the Following Individuals Would Be an Example of Sporadic

Which of the following individuals would be an example of sporadic sibling?

A) John, who visits his aged mother whenever he is in town
B) Alex, who has always helped his sister when it comes to taking care of their aged parents
C) Rita, who tells her younger brother that she wouldn't be able to help with looking after their father during summer break
D) Jake, who has taken up the responsibility of buying his parents medications for them every single week