选出与所给句子划线部分意义相同或相近的一项。

She could play the violin at the age of four. [ ]

A. by 4 years old

B. when she is four

C. 4-year-old

D. when she was four

对随机组运行的主要热工仪表及控制装置应进行现场运行质量检查，其周期一般为（）。