His mother is ill at home, so he has to take care of her today.
A:look like
B:take down
C:1ook after
下图中表示细胞分化的是( )
⑴____A. sixteen B. seventeen C. apple
⑵____A. thirteen B. nineteen C. nine
⑶____A. twenty B. five C. fourteen
⑷____A. eighteen B. crayon C. fruit
⑸____A.eleven B. twelve C. thirteen
交通部门为了限制对公路的破坏,限制车辆对地面的压强不得超过7×105Pa,假设每只轮胎与地面的接触面积恒为0.02m2,则一个四轮运输车对地面的压力不超过____ N.