You can create a button which can be clicked only after all 3 shapes are
animated. By clicking on this button, it will start the next animation.
To do so, you will need to add a button (you can use AutoShape to do so).
Then, add 3 rectangle or oval AutoShapes that cover the button entirely.
Now, select all 3 autoshapes, right click and select Format AutoShapes.
Set them to No Line. Under Fill, set to 99% transparency. This will make
them 'invisible'.
Click Slide Show > Custom Animation.
Add disappear effect to all 3 autoshapes.
Now, have each autoshape triggers under A, B and C respectively.
That is to say, when you click on A, Shape A will animate, and at the same
time, one invisible autoshape will disappear.
Once all three autoshapes disappear, you will be able to click on the button
to continue with the next animation.

See if that is what you want.