题目

合并同类项：－x2－x2＝__________. 答案：【答案】－2x2 【解析】根据合并同类项的法则进行计算即可.－x2－x2=（-1-1）x2=-2x2，故答案为：－2x2.--I listen to music and study at the same time. --Really? Are you ________. [　　] A．jokes B．joking C．joke