Ответ:
1. Why are you angry? - Because I’ve been waiting for a bus for a long time.
2. Why is she crying? - Because she has been peeling the onions
3. Boys, why are your shorts dirty and green? - Because we have been playing football on the grass
4. Why are you sweating? - Because I have been washing the floors
5. Why are your hands so cold? - Because I have been making a snowman in the garden
6. Why are the children so excited? - Because they have been decorating a Christmas tree
7. Why does she look so young? - Because she has been using expensive creams for a couple of years.
P.S. Если хочешь, можешь скоротить have/has been так, как в первом предложении (I, You, We, They + 've been (Пример: You've been living); He, She, It + 's been (Пример: She's been living). Я написал полностью.