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Sind jungs denn dumm - ja sind sie = Are boys stupid - yes they are.
Sind sie wie alt? makes no sense whatsoever in German. You could either ask
Wie alt sind sie/Sie = how old are they/you
sie/Sie sind wie alt = how old are they/you orthey/you are how old
Was sind Klippen = What are cliffs
There are = Da sind
There are = Es sind
Was sind Volkstribunen = What are people's tribunes