If x2+1x^2+1x2+1 is a factor of x4+ax3+bx2+cx+dx^4 + ax^3 + bx^2 + cx + dx4+ax3+bx2+cx+d, which of the following is true?
a=c, b=d+1
a=c, b=d-1
a=0, c=0
a+b=c+d