“引体向上”是近年来各地体育中考新设的男生考核体育锻炼项目,如图所示,为了尽可能正确地估测某位同学引体向上运动的功率时,下列需要测量的物理量正确的是( )
①人体的质量m;②单杠的高度H; ③每次身体上升的高度h; ④做引体向上的时间t;⑤引体向上的次数n;⑥n次引体向上的总时间T.
A:①②④
B:①③④
C:①③⑤⑥
D:①②⑤⑥
Good morning. This is the world weather report. It's warm in Beijing today. Children can play football outside. It's cold in New York. And it's snowy. Children can make a snowman. It's cool in Toronto. Children can fly a kite. It's hot in Sydney. Children can swim in the sea.
City(城市)
Weather(天气)
What to do (做什么)
Beijing
____
New York
Toronto
Sydney
⑴long hair ____ A.
⑵black eyes ____ B.
⑶a thin girl ____ C.
⑷a short boy ____ D.
⑸an old man ____ E.
下图是2005年人口自然变化对比(‰)。与中国相比,发达国家人口死亡率高的主要原因是( )