以下说法正确的是(  )

①油脂属酯类，没有固定熔沸点

②油脂属高级脂肪酸甘油酯，都不能使溴水褪色

③油脂中注入水后能分层且油层在底部

④牛油是高级脂肪酸的高级醇酯，在工业上可用于制硬化油

⑤羊油在碱性条件下水解后可制肥皂

⑥植物油的主要成分是油酸

⑦植物油和矿物油都属于油脂中的油

⑧用硬水洗衣加肥皂后泡沫少是因为产生了沉淀

唐朝时，科举制度得到很大发展，其基本特征是（    ）

引起地方性甲状腺肿（大脖子病）的原因是由于饮食中缺乏（  ）

A：Parks are really important in a neighborhood. ____

B：Sounds good.What can we do?

A：Well, we can pick up garbage(垃圾)．

B：What a great idea! ____

A：Yes, let's ask them to come.We can ask the neighbors, too.

B：____

A：We should bring garbage bags and buckets(水桶)．

B：____

A：Let's volunteer on Saturday.The weather will be sunny.

B：____ 

A：Wear old clothes.We'll probably get dirty.

B：OK.I will tell the others.

A．People must keep them clean.

B．When should we volunteer?

C．What should we wear?

D．Maybe we can invite our friends to help.

E．Let's volunteer to clean up Central Park.

F．I learned a lot from the activity.

G．What should we bring?