Помогите плз . Present Perfect /Simple/ Continuous

 I am busy now. I am doing my homework.
I can help you. I am free now. I have done my homework.
Look! little Johny is washing his bike. He is funny, isn't he.
Little Johny has washed his bike. Now the bike is clean.
I am learning new word now.
I have learnt words and I can go with you.
I have read the story. i think I can answer your questions about it.
I am reading the story now. We can discuss it later.
Mary is busy. She buys a present for her sister.
She has bought a present for her sister. She can go to the bookshop now.