New words：
marathon [ˈmerəˌθɑn] n. 马拉松赛跑
Sample Sentences：
Do you know how long a standard marathon is?
The game turned into a marathon because both teams played well.
Many people from different countries joined the international marathon.
New words：
aid [eɪd]
v.帮助；协助；支持；接济
n.帮助；援助
First Aid 急救
Sample Sentences：
Did you learn any First Aid at school?
The volunteers aided the old people clean their houses.
The Red Cross sent aid to the people in the flood area.
This job would be impossible without the aid of a computer.
New words：
deaf [def] adj. 聋的；不愿听；不去注意
Sample Sentences：
She was born deaf.
He was deaf to all advice.
She was almost blind and deaf, but her heart was full of courage.
New words：
chalk [tʃɔk]
n.粉笔
v.用粉笔写（或画）
Sample Sentences：
The teacher wrote on the blackboard with a piece of chalk.
She wiped the chalk marks off the blackboard with an eraser.
He chalked a math problem on the blackboard and asked us to solve it.
New words：
unit [ˈjunɪt] n. 单元；单位
Sample Sentences：
The basic unit of length is the metre.
The basic unit of society is the family.
We are studying Unit 5 in the biology textbook.
The team was divided into smaller working units.