Using paragraphs

This task is about breaking a text into paragraphs.
a)  Ina wrote a story about what she did on Saturday. She wrote a good story but she forgot to use paragraphs.
Read Ina's story. Then go back and draw a line (like this: ) in each place a new paragraph is needed.
The first one has been done for you.
 

Ina

On Saturday morning we got up really early and watched cartoons on TV. There was this really funny bit on 'What Now' when Mike tipped a bottle of milk over Tina's head. I pretended to tip a bottle of milk over Sam's head but he didn't laugh. At nine o'clock Mum got up. We got told off for making a mess in the lounge. It wasn't even that messy. There were just a few cushions and some Lego on the floor. There was some milk on the floor too, but hardly any. Mum said we had to clean everything up. I ended up cleaning most of it up by myself. Sam just pretended to help. Then we went to swimming lessons. I am in the Sharks group and Sam is in the Tadpoles. I am the best at backstroke in our group. My swimming teacher said I might be able to go in the inter-club swimming competition. After swimming we went to McDonalds for lunch. Yum! I had a Big Mac Combo and Sam had a Cheeseburger Combo. We got some stickers with our meals. Mum had a coffee. She doesn't like McDonalds' food that much. When we got home Sam and I made a hut in the basement under our house. We got some old furniture and set it up. It looked really good but it was quite dark. We had macaroni cheese for tea. I hate macaroni cheese! I call it macaroni slime. Mum said I didn't have to eat it all but I had to eat some. I ate a tiny bit. But then I ate lots of ice-cream for pudding so I wasn't hungry at all. 

 
b)  When do you need to start a new paragraph in your writing?