在等式的括号内填上恰当的项：x2-y2+4y-4=x2-______．
根据添括号的法则可知，原式=x2-（y2-4y+4）．
故答案是：（y2-4y+4）．
—I called you at 5:00 yesterday afternoon. But there was no answer. Where were you?
—I _____ in the supermarket. [ ]
A. was shopping
B. am shopping
C. have shopped
D. do shopping
溶于非水介质的聚乙烯油漆及清漆
