题目内容
（请给出正确答案）
[主观题]
It was in 2005 ____ we began to introduce this new technique into our company.A which
It was in 2005 ____ we began to introduce this new technique into our company.
A which
B then
C when
D that
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A．覆盖区域面积
B．覆盖效果
C．设备成本
D．施工难易程度
