Just as the uranium series is called the “4n + 2” series, the thorium series can be called the “4n” series and the actinium series the “4n + 3” series. A “4n + 1” series has also been established, with ²⁴¹₉₄Pu as the parent nuclide. To which series does each of the following belong? 

(a) ²¹⁴₈₃Bi;

(b) ²¹⁶₈₄Po;

(c) ²¹⁵₈₅At;

(d) ²³⁵₉₂U.