New words：

avail [ə'veil] v.有用；有帮助；有益
to no/little avail 没有什么效果；不成功
of no/little avail 没有什么用处；没有用

Sample Sentences：

This medicine is of no avail.
We tried to keep him alive but to no avail.
The medicine did not avail against the disease.
He tried and tried but all his efforts were of no avail.

New words：

within [wi'ðin] prep. 在(某段时间、距离或范围)内, 在…里面

Sample Sentences：

I'll be coming within an hour.

They finished the house within half a year.

You should receive a reply within seven days.

Several cars are available within this price range.

available [ə'veiləbl] adj.可获得的；可购得的；可找到的；有空的
avail [ə'veil] v.有用；有帮助；有益

New words：

pupa ['pju:pə] n. 蛹
ladybug ['leidibʌg] n. 瓢虫

Sample Sentences：

One ladybug can eat up to 5, 000 insects in its lifetime.
Within a week or two, the pupa becomes an adult ladybug.
It takes at least eight days for a fly to go from an egg to a pupa.

within [wi'ðin] prep. 在(某段时间、距离或范围)内, 在…里面

New words：

silk [silk] n.丝绸；（蚕）丝；丝织物

Sample Sentences：

This kind of paper was as soft and light as silk.
China is famous for its silk and tea in the world.
It was a stopping point on the famous Silk Road between the East and the West.

New words：

cocoon[kə'ku:n]

n.茧；软罩；保护膜；防护层
v.把…包围起来保护；（用…）完全保护起来

Sample Sentences：

Most worms cocoon in winter.
A cocoon is a kind of silk covering made by an insect.
The children tore the cocoon open to see if there was a pupa.
We were warm and safe, cocooned in our sleeping bags.

silk [silk] n.丝绸；（蚕）丝；丝织物