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 condition must hold?
a=c and b-d=1
a=c and b-d=-1
a=c and d=b-1
a=-c and b-d=1