Paul observes that ab=ac and concludes that ab and ac must be tangent to the circle. what is wrong with paul's reasoning?

The complete question in the attached figure

we know that
the triangle AOB is congruent with triangle AOC
because
AB=AC
OB=OC-----> the radius of the circle
The OB side is common
but

there is no additional information that allows me to calculate the OBA angle to determine if it is a right angle

therefore 

the answer is the option
C.There is no indication that AB and AC are perpendicular to the radii at the points of intersection with the circle.

Bis your answer rot d