he is a boy of ten 3Q

英语语法请教
Their experiment (has)stretched over a period of ten years.
那个has加上去可以吗?

eight of ten seconds 是什么意思拜托各位大神
eight of ten seconds 是什么意思?完整的句子是：And if you start feeling frisky and you have eight of ten seconds before work,you know where to find me.

语法好的进来
__a boy of ten,he started working to support himself.
A Being
B When still
C Because
DWhile
选什么?理由
什么情况下可以省略?为什么不能选A

many people at the age of ten 和many people in their teens这两个意思一样吗,前面的表达方式对吗

用单词适当形式填空：1.At the age of ten,he showed much__(interesting) in maths
2.The dictionary is a little expensive,but it is very__(use)
3.Among those__(invent),that is the most important one in his life
4.I felt__(surprise) at the news
5.Jack was ten minutes__(later) for school
6.The earth__(turn) around the sun
7.Look,Wang Fang__(swim) fastest in the group
8.--Where__(be) the students? ---They__(go) over their lessons in the classroom.They__(have) a maths test this afternoon
9.His sister__(not like) singing
10.He usually__(get) up at six every morning.But he__(get) up at half past six tomorrow morning
二.改句子
Give him the cake.改为否定句
2..This T-shirt costs (fifty yuan)对括号里提问
3.I'm going to do some reading this evening. He's going to do some reading this evening.合并成一句
__ he __ I are going to do some reading this evening
4.We are going to see you (next week) 对括号里提问
5.The year 200 is a leap year.改为反意疑问句 The year 200 is a leap year,___ ___?

They （not be） from japan,but they of ten （speak） japanese
还有You must execise to ____ ____ ____ _____(保持健康）

麻烦解释下这个英语的用法
“Mr Black has a boy of ten.”中的a boy of ten.有这个用法的吗?

how many groups of ten 和how many ten 的区别
可能我的问题没有说清楚,我是想问下,how many tens and how many ones are there in the number forty-three与how many groups of ten are there in 43 and how many ones are left over in 43的区别.
它们同样说的是43里面有几个10,多少个1,为什么有的仅用how many tens ,而有的用how many groups of ten