A:x2﹣y
B:x2+2x
C:x2+y2
D:x2﹣xy+y2
Why not send an email to her instead of ____ (reply) to her letter?
找出不同类的词,把字母代号填在横线上。
① ____ A. A. five B. four C. face D. nine
② ____ B. A. write B. ride C. red D. run
③ ____ C. A. short B. shorts C. dress D. blouse
请用反证法证明:如果两个整数的积是偶数,那么这两个整数中至少有一个是偶数.