请简要说明为何运动能提高心脏功能。
参考答案：
长期坚持体育锻炼可提高心肌对能源物质的转运和利用，使心肌纤维中收缩蛋白增多心缩力增强，血肌收缩速度增快。
根据对话情景，填入恰当的单词。
A: What do you usually do 1 school?
B: I 2 my homework first, then do some chores.
A: Really? Do you 3 doing chores?
B: Yes, very much I'd like to 4 supper, because I like to cook. Do you like to make your bed?
A: No, not really. It's 5 .
B: I don't think 6 . It's a good habit to make the room 7 and tidy.
A: Maybe you're right. I will do as many 8 as I can.
为什么说冷战后世界的多极化在曲折中发展？
