It was a boring and dull afternoon．Olivia had to work on a project for school about invention with wheels．
She couldn't think of any ideas．
"What am I going to write，Eliza？"she asked her little sister．Eliza didn't answer．
"I'm going to go for a bicycle ride．That will help me think．"
Eliza followed her．
Go inside，Eliza．Tell Mom I'll be back soon．"
Eliza was an obedient four﹣year﹣old girl．She always listened to Olivia．
"Be a good girl，Eliza．"Olivia closed the gate and rode away．She didn't see the gate swing（摇摆） open behind her．
Olivia went riding fast down the hill from her house．It was exciting to move so quickly．She was slowing down to make a turn when she saw someone behind her．
"Eliza!You are following me the whole time!You didn't listen!And I must have forgotten to lock the gate!"
Then she saw that Eliza was crying and walking difficultly with a wounded knee．
"I fell down，"said Eliza．"My knee hurts!""Oh，no!You won't be able to get up that hill!"
Olivia knew it was foolish to leave her sister alone outside．What were they going to do？Olivia started to get scared，but she knew she must be brave and find a way to get home．Then she saw an old wooden carriage by the path．The carriage was so old that it was broken when she picked it up，but the four metal wheels and two axles （车轴） were still strong．Then she found an old straw mat （垫子） and some strong wire．She tied the mat between the two axles with the wire．Then she tied the new cart to the back of her bike seat．
"Come on，Eliza!Get on the cart．"
Olivia got on her bicycle and started to ride．It was hard to get up the hill，but she decided to get home．Finally，they arrived．
"We're home，"said Olivia．"And I have an idea for my wheel project．I'm going to write about my new invention﹣a little sister carrier!"
