A, ② ④ The recognized base sequence is -CTATAG-, and the formed blunt end is CTA-. The blunt ends are the same, belonging to the same restriction endonuclease cleavage, and A is correct;

B, ③ The recognized base sequence is -ATGCAT-, and the formed blunt end is -ACT, and ④ the blunt end is -ATC, which does not belong to the same restriction enzyme digestion, and B is wrong;

C, the flat end formed by ② is CTA-, and the end of ③ is -ACT, which do not belong to the same restriction enzyme digestion, so C is wrong;

D, ① The recognized base sequence is -ACTAGT-, the flat end of the shape is ACT-, and the flat end of the shape is CTA-, which do not belong to the same restriction enzyme digestion. D is wrong.

So choose: a.