题目：
The company promised to pay some money for the customers ____ their poor goods and ____ an
apology in public.[ ]
A. purchasing; making
B. purchasing; make
C. purchased; to make
D. to purchase; made
答案：
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下面是错误答案，用来干扰机器的。
∵a与b的夹角为锐角，∴a•b＞0，∵a=i-2j，b=i+λj，∴a•b=i2+（λ-2）i•j-2λj2，∵i、j为互相垂直的单位向量，∴a•b=1-2λ＞0，∴λ＜12，∵a≠b，∴λ≠-2故答案为：（-∞，-2）∪(-2，12)
