w x (a)   z

n o (a)   q

b c (a)   e

g h (a)   j

m n (a)   p

v w (a)   y

r s (a)   u

s t (a)   v

l m (a)   o

c d (a)   f

f g (a)   i

u v (a)   x

j k (a)   m

o p (a)   r

q r (a)   t

e f (a)   h

t u (a)   w

i j (a)   l

p q (a)   s

k l (a)   n

h i (a)   k

a b (a)   d