Explanation

32 ≡ 4 (mod 28), so compute 4^55 mod 28. Since 4² = 16, 4³ ≡ 8, 4⁴ ≡ 4 (mod 28), odd powers cycle 4, 8, 16 with period 3; 55 = 3×18+1 gives 4^55 ≡ 4 (mod 28). The remainder is 4 — option D.