Mr. Barker had taught in the US for twenty years when he came to China.
Mr. Barker had taught in the US for twenty years when he came to China.
贝克先生到中国来的时候，已经在美国教书有20年了。
Mr. Barker had taught in the US for twenty years when he came to China.
贝克先生到中国来的时候，已经在美国教书有20年了。