Which underlined word is an interjection? woo-hoo! i just got a new mountain bike! bike woo-hoo new mountain

Dear Annie,

I am very delighted to write to you this letter. Thank you for letting Uncle Charles giving me the English text book.How is he doing.i hope you and your family are doing well by the Grace of God and how is school today?

The main reason I'm writing to you this letter is because of the book you lent to me last week.it was very good and useful to me.It helped me in so many ways and some are:

1.It helped me in my English test:there was a class test on last week Monday and I needed that book badly and when I got it I was just delighted when I got that book.I learnt it very well and when it was time for the test I wrote it without struggling.

2.it also helped me in my homework:our teacher gave us homework and he said we should look for that type of English text book which is the New student companion that you lent me and when I went home I took it and did it easily

Annie thank you very much for the book you lended me that day because it helped me very much.Please extend your greetings to mum and dad for me.

Yours lovely,

Emma