The dots and dashes in every sq., when decoded as Morse code, spell out “THIS IS A POLYBIUS SQUAR”. From this, we will assume that the proper selection is reply B, because it correctly finishes the message as “THIS IS A POLYBIUS SQUARE”.

With a little bit of assist from the trace, which mentions the phrase “common”, I then checked out the entire squares with common polygons within the grid. The corresponding letters from the Polybius sq., so as of the variety of sides within the common polygon, offers the pbrase “OF THE”, which doesn’t look like a solution. Studying the morse from the reply decisions usually offers “NEON”, however reordering the common polygons by aspect quantity and extracting the morse once more offers “NONE”, which appears related. Each phrases appear near spelling out “NONE OF THEM”, which can reply the query “Which of those is the reply?”, however M’s form is a non-regular rectangle, so it appears doubtful.

I’ll hold this information right here for comfort’s sake.
Message:
THIS
IS A
POLYB
IUS S
QUARE
Polybius sq. (“I” is definitely “I/J”):
ABCDE
FGHIK
LMNOP
QRSTU
VWXYZ
Variety of sides (“A” represents 10 for spacing causes):
2A017
40634
34230
21352
43106
Letters sorted by form:
0 = CGPY
1 = DRX
2 = ANQU
3 = ILOSW
4 = FKMV
5 = T
6 = HZ
7 = E
10= B
Polybius viable numbers:
21434342321352431