RBS2206与RBS2202相比，少了以下哪种RU单元？（）
A、TRU
B、ECU
C、PSU
D、CDU
参考答案：B
分解因式：a2-b2-2a+1
His plan was such a good one _____ we all agreed to accept it. [ ]
A. so
B. and
C. that
D. as
