Even though manufacturers and retailers can forecast aggregate demand with some certainty=It has not prevented companies from predicting aggregate demand with some certainty.
定位句：However, new research concerning supplier relationships in various industries demonstrates that the widespread assumption of Western managers and business consultants that Japanese firms manage their suppliers primarily through strategic partnerships is unjustified. 另外拜托对转折词敏感起来ball ball我自己了
(1)+(2) Both 4r+9−s=04r+9−s=0 and 4r−6−s=04r−6−s=0 cannot be true (simultaneously), as 4r−s4r−s can not equal to both -9 and 6, hence 3r+2−s=03r+2−s=0 must be true. Sufficient.
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错选D。没注意challenge这个词。