He began to work there （ ）.A.on his fifty B.at the age of fifty C.when he fifty D.in his fifties选D,but为什么?每个选项的区别是什么?PLEASE````````

My brother began to work when he was sixteen. My brother began to work ---- ---- ---- ---- sixteenHe is the oldest teacher in the school.He is ----- ---- ---- ---- teacher in the school. he went into his room, turned up the light and began to work这句话对不对 He began to run () restaurant after he was out of () work A、a;the B、a;/ C、/；/ D、the；the He began to work again because he had from a bad cold He was given a for winning the he began to work at__dawn every morning because he was heavily in ___debta / /b / thec the /dthe the He began to work in his thirties是什么意思? It was in 1990 ------he began to work.It was 1990 ------he began to work.用when/that填空 He began to work at the age of 12.at the age of 12.画线,对划线部分提问 The old man began to work ____ he had A.short rest.A.when B.while C.until D.after After ＿(test) the machine,they began to work. He began to work three years ago (改同义句)He ______ _______ _______ in the city for past three years He began to work there____.A.on his fifty B.at the age of fifty C.when he fifty Din his fifties Not until three years ago,did he begin to work outside.这句子中为什么不用 he began to work he stepped into the office, ____ down and began to work at once A sitting B to sit C having sat D sat He went into his room, the light and began to work.A. has turned on B. turned off C. turned on D. has turned off 用old,my,was,to,father,he,years,began,when,when,work,twenty连词成句 His father began to work as___as he was seventeenAold Bearly Cfar Dbefore哪个为什么? His father began to work since he was seven years old.这个句子有错吗?