题目

       Robin broke his left leg in the basketball match last week, since then he __________ in bed.      A. lay                    B. has lain                     C. laid                          D. has laid 答案：B下列命题中，真命题的是（　　）A．若x2=y2，则x=yB．若|a|=|b|，则a=bC．若xy=1，则x，y互为倒数D．若a+b=0，则ab=-1