某规模猪场，初产母猪流产，产死胎、木乃伊胎，或产出病弱仔猪;死胎皮肤充血、出血、水肿或脱水;经产母猪未见流产。.防控该病最有效的疫苗接种时间是
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Willyou_________playingbasketball?
IntheendI______agoodefforttopasstheexamination.
Shewouldratherhavearoom__________thansleepwithhersister.
Hisbackacheisonly_________fornotwateringtheflowers.
实对称矩阵所，如下图，对应的二次型f(x1,x2,x3)=______