v表示速度,t表示时间,s表示路程.
s=____,v=____,t=____
家兔门齿的主要功能是撕裂食物。( )
Our teachers have been with us for nearly three years _______ we came to junior high school. We should thank them for what they have done for us.
在有性生殖过程中,双亲通过生殖细胞分别向子代传递了( )