Jim is from New York(纽约). His home is near the school. So he often goes to school by bike. Every day it takes him about fifteen minutes to get there. He always gets to school on time(准时).

    Mary is a student of a middle school in Tokyo（东京）. The school is far from her home. Every day she has to go to school by subway. It takes her about forty minutes, she often gets up very early because she doesn't want to be late for school. She is a good student.

    Jenny's home is in London. It is far from her school. She usually goes to school by bus. This kind of bus has two floors. It takes her an hour every day. She must get up very early every morning. She often gets there early.

    Tom is a student of a middle school in Iceland（冰岛）. There is snow all year around. So he usually goes to school by sledge（雪橇）. It takes about twenty minutes to get there. He is sometimes late for school.

①求甲对地面的压强p_甲．

②求乙容器内水面下0.1米深处的压强p_水．

③将甲浸没在乙容器的水中后（无水溢出），若乙容器对地面压强的增加量是水对乙容器底部压强增加量的2.7倍，则求甲的密度ρ_甲．

如图表示鸟卵的结构，其中能发育成雏鸟的结构是（   ）