The best way to reveal visual aids during your presentation is to make them visible
a. throughout the duration of the speech.
b. only at the beginning of your speech.
c. only at the end of your speech.
d. by passing them around, one-by-one.
e. only when you refer to them.

E. Only when you refer to them

Explanation:

Only reveal visual aids when you are referring to them in your talk and when they are directly relevant to the topic at hand. After you are done referencing them, take them down so the audience is not distracted from your words.

  b.

there are isolated pockets of farming, generally around rivers and oases, which are used for irrigation.

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