"Have you already read this flyer?"
Translation:כבר קראתָ את העלון הזה?
Is it wrong to start the sentence with אתה? (I realize that the verb makes it unnecessary.) Also, the answer seems to insist on the vowel under the תָ. That seems wrong if we have no subject, since the subject could be את.
It is not wrong to start with אתה, but it would feel emphasized, Have you already read? As for the vowel, it's true both קראתְ and קראתָ are correct and I'm sure both are accepted in addition to no nikkud, which is ambiguous.