A series is given with one term missing. Select the correct alternative from the given ones that will complete the series.
BB, DZ, GW, KS, ?

Let's separate the series into two parts (first letters and second letters):
First Letter Series:
B→D→G→K→?

B(2)+2=D(4)

D(4)+3=G(7)

G(7)+4=K(11)

Following the pattern +2,+3,+4, the next step must be +5:
K(11)+5=16=P

Second Letter Series:
B→Z→W→S→?

B(2)−2=Z(26)

Z(26)−3=W(23)

W(23)−4=S(19)

Following the pattern −2,−3,−4, the next step must be −5:
S(19)−5=14=N

Combining both results, we get PN.