5.  Will you wash the cups. please,? But I have already washed them- Present Perfect - смысловой глагол в третьей форме

6.  It is the funniest picture I have ever seen - превосходная степень прилагательного - суффикс  est 

7. I didn't meet him two days ago - у Вас - 2 days ago - два дня назад - значит, Past Simple

8. It's the most diffictult  text we have ever translated - есть слово ever - когда-нибудь - значит, Present Perfect - нужен вспомогательный глагол have 

9. Has he ever been to Suzdal? - с местоимением he употребляется глагол has

10. Have you ever been to an art gallery? - артикль an потому что существительное начинается с гласной буквы

Verified answer

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5. Would you wash the cups please?

But i have washed them

6. It's the funniest picture i have ever seen.

7. I I didn't meet him two days ago

8. It's the most difficult text we have ever translated.

9. Has he ever been to Suzdal?

10. Have you ever been to an art gallery?