Which letter replaces the question mark ?

In this type of letter series, capital letters are classified by their visual form — letters made entirely of straight strokes (such as E, F, H, I, L, T) versus letters that contain at least one curved stroke (such as B, C, D, G, J, O, S, U). The series moves forward through the alphabet but skips any letter from the straight-line-only group, so only letters from the curved group appear as terms.

1. The given terms are B, C, D, G — each of these contains a curved stroke, placing them in the curved-letter group the series is built from.

2. Moving on from G, the next two letters in the alphabet are H and I. Both are formed only of straight lines, so under the rule they are skipped.

3. The next letter after I is J, which contains a curved stroke at its base, so it qualifies and becomes the next term.

The same rule already operated between D and G, where the straight-line letters E and F were skipped in exactly the same way H and I are skipped here — confirming the pattern holds consistently. Hence, the letter that replaces the question mark is J.