Concept:
In letter series, observe each position separately and check how letters change.
Series:
\[
BPJE,\; BQDH,\; BRCF,\; BSBD
\]
We analyze column-wise.
Step 1: Check the first letter.
First letters:
\[
B,\; B,\; B,\; B
\]
No change.
Next first letter:
\[
B
\]
Step 2: Check the second letter.
Second letters:
\[
P,\; Q,\; R,\; S
\]
Pattern:
\[
+1,\;+1,\;+1
\]
Next letter:
\[
T
\]
Step 3: Check the third letter.
Third letters:
\[
J,\; D,\; C,\; B
\]
Pattern moves backward.
Next expected letter:
\[
A
\]
Step 4: Check the fourth letter.
Fourth letters:
\[
E,\; H,\; F,\; D
\]
Pattern after reduction gives next:
\[
B
\]
Step 5: Form the final term.
Combining all:
\[
B + T + A + B
\]
\[
= BTAB
\]
Hence, the correct answer is:
\[
\boxed{BTAB}
\]