当x=____时，分式 $\frac{x^2-1}{x+1}$ 的值为0．

— Mom, my classmates are playing outside. Can I join them?
— Not until your homework       .

将不同植物的三个未发生质壁分离的细胞置于同一浓度蔗糖溶液中，形态不再变化后的细胞如图所示．则有关各细胞液的浓度判断正确的是（  ）

．This January will be very precious for us by which time we _______reviewing Senior Book I.                                                                                                        

This is our school.