Since
∠
AOB
is a right angle, it is
90
∘
.
∠
AOB
is supplementary to
∠
BOC
, so
m
∠
AOB
+
m
∠
BOC
=
180
∘
. By the substitution property of equality,
90
∘

+
m
∠
BOC
=
180
∘
. Applying the subtraction property of equality,
m
∠
BOC
=
90
∘
.
What statement is missing from the proof?
A.

∠
AOB
and
∠
BOC
form a linear pair.
B.

∠
AOB
and
∠
DOC
are vertical angles.
C.

∠
COD
and
∠
AOD
form a linear pair.
D.

∠
DOA
and
∠
BOC
are vertical angles.