Question

why does Helen say that Christmas after miss sullivans arival was a great event

Answer 1

Hey!!!!
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The first Christmas after Miss Sullivan arrival proved to be a great event because everyone in the family had prepared surprises for Helen. However what pleased her the most was that she and Miss Sullivan also prepared surprises for everybody else. The mystery that surrounded the gifts was Helen's greatest delight and amusement. Her friends did all they could to excite her curiosity by hints and half-spelled sentences which they pretended to break off in the nick of time. Miss Sullivan and Helen kept up a guessing game which taught her more about the use of language than any set lessons could have possibly accomplished. Every evening, seated around a glowing wood fire, they would indulge themselves in this guessing game which increased in excitement as Christmas approached. 
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Hope it helps!!!! :)

Answer 2

The first Christmas after Miss Sullivan arrival proved to be a great event because everyone in the family had prepared surprises for Helen. However what pleased her the most was that what surprise had sullivan prepared for helen  as this was their first christmas