在边长为a的正方形中挖去一个边长为b的小正方形(a>b)[如图N43(1)],把余下的部分拼成一个矩形[如图N43(2)],根据两个图形中阴影部分的面积相等,可以验证( ) (1) (2) 图N43 A.(a+b)2=a2+2ab+b2 B.(a-b)2=a2-2ab+b2 C.a2-b2=(a+b)(a-b) D.(a+2b)(a-b)=a2+ab-2b2 答案:C When was _____ that the general manager left for Japan? A. he B. it C. that D. since