The boy started playing the piano when he was four years old.(同义句）

题目

The boy started playing the piano when he was four years old.(同义句）
The boy started playing the piano ___ ___ ___ ___ ___ .

答案

正确答案：填at the age of four
即：The boy started playing the piano at the age of four.
翻译：这个男孩四岁时开始弹钢琴.
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