If a + b + c + d = 4, then the value of 1(1−a)(1−b)(1−c)1(1−a)(1−b)(1−c) + 1(1−b)(1−c)(1−d)1(1−b)(1−c)(1−d) + 1(1−c)(1−d)(1−a)1(1−c)(1−d)(1−a) + 1(1−d)(1−a)(1−b)1(1−d)(1−a)(1−b) is?

• A. 0
• B. 1
• C. 4
• D. 1 + abcd