If none of two lines among the following three lines

ax + by -(a + b) = 0

bx - (a + b)y + a = 0

and (a + b)x - ay - b = 0

are parallel then the lines

(A) are concurrent

(B) from a right-angled triangle

(C) form an equilateral triangle

(D) form a triangle with circumcentre(a + b,a + b)