He was fond of play, but he had been taught to make himself useful, and to do as he was bid.
请问这句话中为什么最后是as he was bid,而不是as he is bid?
 《高考英语备考1号·速效编》
						《高考英语备考1号·速效编》
					 《高考英语备考1号·写作编》
						《高考英语备考1号·写作编》
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						《高中英语晨读晚记》
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						《高中英语错题笔记》
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						《零起点考大学英语》
					