Question

fill up To preview the animation effect click on .....button on custom animation pane

Answer 1

The answer is play button...
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Answer 2

Answer:

The answer to this question is a play button.

If one wants to preview any animation the play button is to be pressed to see the action and the effect.

Preview in animation helps to adjust the speed of the slides to change so that the best effect can be experienced through a method of trial and error.