A:退耕还林效果显著
B:未利用土地增加
C:粮食播种面积增加
D:其它农业用地增加
— Tom says he is too tired to go on.
— He can't. He ________ for an hour.
Would you mind down the music? I'm trying to sleep.
小丽同学的质量为45kg,她每只鞋接触地面的面积为1.5×10-2m2,她站在了一块泥地上,为了不让脚陷进泥地,她在水平泥地上放一块重力为200N的木板,当她双脚站立在木板中央时,地面受到的压强为325Pa。求: