几道英语题没想通,求讲解In some places,little()to make smoke clean.为什么一定

几道英语题没想通,求讲解
In some places,little()to make smoke clean.
为什么一定是is done 不能是 has done
when the dog was only () old,he saved a drowning boy.
为什么是a year and a half 而不是 one and half a year
There are () in our class
为什么是Wangs而不是 the Wangs?
there're () fish sold at this market.
这里怎么会是a great number of?fish没+s来着……要不是我题抄错了?
people often go to () church on Sundays in western countries.
为什么括号里不用填a?
Do you know anything about Solomon,() king of ancient Israel?
为什么括号里不用填the
() Mrs.Williams () her husband has been to Thailand.Either of them can be your guide.
为什么一定要not only,but also 不能是 either or