Finding right angles

This task is about angle properties.
Name all the right angle(s) in each of the following diagrams.
The centre of each circle is labelled O.

Question 1Change answer

a) 
diagram of a circle and lines
Right angle(s):   

Question 1Change answer

b) 
diagram of a circle and lines
Right angle(s):   

Question 1Change answer

c)
diagram of a circle and lines
Right angle(s):